Regular Caller

In action, adventure or drama shows, the protagonists need a Call to Adventure. Every. Single. Episode. In a series with low seasonal fluidity, a single call may last for an entire series, or at least a few episodes. But if Failure Is the Only Option, then don't be surprised to see a Call happen once a week. Originality is hard, so expect to see writers fall back on the same Call frequently. When the same Call comes on a semi-regular basis or even every episode, this is a Regular Caller.

When done well, it ties into the premise of the show and follows logically, and when done poorly it comes off as contrived and risks breaking suspension of disbelief. This trope is ubiquitous in things like Police Procedurals, Medical Dramas and Courtroom Dramas.

The Magnetic Plot Device can overlap with the Regular Caller, however the Magnetic Plot Device is usually just an in universe justification for the Regular Caller. The Bat Signal is one specific kind of Regular Caller.

Examples of Regular Caller include:

Anime and Manga

In Puella Magi Madoka Magica, Kyubey is insistent to the point of being annoying on the whole 'Sign a contract with me and become magical girls' thing. Even when the girls are witnessing horrifying and traumatic things happening to those who decided to sign such contracts!
- Quoting the character sheet: "The call is on reversed charges, though. With international call prices."

Comic Books

In Sam and Max and its various adaptions, every case is preceded by a call from the mysterious Commissioner.
In the Silver Age, Superman often received a Call to Adventure in the form of Jimmy Olsen's signal watch. That, or Perry White would send him to investigate something as Clark Kent.
As mentioned above, the Bat-Signal is a classic example.

Literature

In The Dresden Files, there seems to be some supernatural crisis occurring on the streets of Chicago every six months or so. Of course, this is eventually justified in that many of these events were apparently due to the REAL Big Bad's (whoever that or they are) Evil Plan to... we're not entirely sure yet, make Harry's life a living hell? It helps that Harry has mentioned that magic and dark forces have been getting stronger of late.
In the Eternal Champion stories, Ekrose (a.k.a. Elric) is always called to a different war on a different world, only getting some measure of peace for a short period of time.
Harry Potter gets a new call every year, and it almost always has something to do with the current Defense Against the Dark Arts teacher. (The reason the subject gets a new teacher every year is finally explained toward the end of the series: Tom Riddle put a curse on the position after he was turned down for it himself, so that whoever got the job would have something unpleasant happen to him.)
In Wearing the Cape, Crisis Aid and Intervention Heroes (the setting's city superteams) aren't patrolling freelance crimefighters. Instead they are special services contractors tied into a city's emergency-response department, and most of Hope/Astra's action-scenes start with a summons from Dispatch.
Michael from the Knight and Rogue Series finds one grand adventure (a.k.a. some crime to investigate) per book.

Live Action TV

In Stargate SG-1, the main Regular Caller is referred to as an "Unscheduled Offworld Activation". The Unscheduled Offworld Activation happens in almost every episode (except clip shows). The other main one is the Asgard beaming one of the main cast members aboard their spacecraft and requesting their assistance, usually while they are in the middle of something important.
Charlie's Angels. "Good morning, Angels!"
Mission: Impossible. "Good morning, Mr. Phelps."
UFO. SHADO sprang into action whenever SID (Space Intruder Detector) detected a Flying Saucer approaching from space.
Seven Days: (Background: Parker is the only one who can pilot the time sphere and when he travels to the past he and the sphere disappear from the past's present.) In one episode the sphere disappears but Parker's still here! Maybe Parker was unable to travel and it's Donovan, the backup chrononaut? No, he's here too. It turns out it's someone from further in the future when they are able to send the sphere much more than seven days back.
Burn Notice: Every single week early on in the series, Michael is either tricked, guilted, or goaded into undertaking a mission that has nothing to do with himself. More recently his sociopathic "handler" just hands him missions.
Chuck: The General gives the team their missions, usually.
- Or Chuck will happen to flash on something relevant and then the General gives the team their mission. Although this was common at the beginning, it petered out to the point where it hardly happens at all after he gets the Intersect 2.0
Quantum Leap had Sam simply Leap into a new time period when he was done fixing the last one. Oh boy.
Leverage: An aggrieved party usually seeks out the services of the team.
NCIS: Another dead Naval officer.
In Series 5, Doctor Who has started having literal calls to adventure, when the Doctor gets a phone call in the TARDIS from some other part of space and time. Winston Churchill has done it twice (the second time getting re-routed to River Song because the Doctor didn't pick up), and so has an unnamed monarch calling about "an Egyptian goddess loose on the Orient Express. In Space."
- This isn't the first time; Martha gives the Doctor her phone at the end of the Series 3 finale "Last of the Time Lords" for precisely this reason.
- Bonus points since the TARDIS is Mode Locked into a police callbox.
Filmations Ghostbusters, the original Live Action TV version : "Good afternoon, Ghost Busters. This is Mr. Zero..."

Video Games

Every couple generations, Ganondorf tries to take over Hyrule. Coincidentally, every time he tries, there's a green-shirted elf around who is the only one able to stop him. Specifically, he's sometimes the Hero of Time, but more recently he's going as The Wind Waker, or, "The Hero Formerly Known as the Hero of Time."
- Actually, there was that one time... He managed to Take Over the World, but the gods flooded Hyrule.
"Reimu, you must investigate the scarlet mist!" "Reimu, you must investigate why Spring Is Late!" "Reimu, you must investigate the false moon!"... and so on. If it's not for Yukari's (or Marisa's) once-per-episode urging, Reimu will never do her job. It's All There in the Manual, though.
Adol Christin of Ys. His attitude can be summed up by: 'Ok, saved this place. Time to go look for the next place in need of saving.' While he often finds or is granted magical talismans by grateful locals and goddesses, he either returns them when he's done with them or they fall victim to his bad luck with ships. He's done this seven times, not counting spinoff and Alternate Universe / Canon Discontinuity games.

Web Comics

The whole premise of The Inexplicable Adventures of Bob is to Lampshade this. Bob is always minding his own business when some new "call" comes completely out of nowhere and for no apparent reason. Most frequently, The Call crashes into his roof.

Western Animation

Captain Scarlet has the Mysterons announce their latest plot to Spectrum, prompting the episode's adventure. Sometimes Spectrum's reaction to the warning was a key part of the Mysterons scheme.
Inspector Gadget: ...This message will self destruct. Don't worry chief, I'm always on duty.]]
Futurama has Professor Farnsworth say "Good news, everyone!" to his employees.
Thunderbirds has Thunderbird 5 monitoring worldwide communications, to allow them to react to emergencies even though they were a secret organization with no method of direct contact.
Superfriends (1973). The title heroes were called into action by either (a) an emergency signal from the TroubAlert computer, (b) a message from Colonel Wilcox or (c) both.
The Powerpuff Girls has the team being called by the mayor and a phone with a flashing red light going off.
'Hey Wade, what's the sitch?' from Kim Possible pretty much kickstarts every adventure.
Every time the alarm goes off on Time Squad.
Wonder Pets: "The phone, the phone is winging... there's an animal in trouble!"
in Swat Kats, Deputy Mayor Callie Briggs has a communicator to summon the titular heroes.