Oddly-Overtrained Security

They are elite, and have the best equipment and training their government can provide. They're carrying rifles and wearing body armor and helmets, looking ready for battle. If you ever meet one, be prepared to quake in your boots and change your shirt from the nervous sweat as they step out of their vehicle, walk over, and ask...

""License and registration, please.""

Despite being the best of the best, they are also everywhere and doing every security oriented job, including traffic cop. The reasons are various - laziness or lack of research on the part of the writers, Rule of Cool, conservation of animation or costuming budget, etc.

This can operate at different scales; it would be unusual to see special operations soldiers guarding every US Embassy (normally guarded by Marines), just as it would be unusual if every security guard, police officer, and traffic cop was a Marine, every clerk and retail worker was a cop, or darn near everyone was wearing a combat uniform.

Contrast The Guards Must Be Crazy.

Anime and Manga

 * An episode of Ghost in the Shell has Togusa go undercover to investigate a facility for youths suffering from "cyberbrain addiction". The first sign something's up is the presence of an 8 foot tall cyborg covered in solid metal armor.

Film

 * In Star Wars it's averted by the actual films which are fairly consistent about noting that Stormtroopers are elite troops (we only see them so much because we see Vader so much), but the Expanded Universe tends to depict them as cannon fodder that are all over the place doing everything, especially videogames.
 * The second Men in Black film sees J re-recruit K from his retirement at a post-office. The retiree deals with a spilled coffee by issuing orders like he's containing a nuclear breach.

Web Comics

 * Questionable Content uses it with a good amount of lampshading, when a lieutenant on a space station is charged with carrying out standard security checks on new arrivals. This is despite the presence of an AI that can do molecular scans on them and their coming from a spaceport, which presumably has security of its own.
 * A recent story arc revealed that a recent court decision banned AIs from serving in the military, to the point of requiring purpose-built military robots that were already on active service to be immediately discharged even though many of them wanted to stay in.

Web Original

 * In the Batman Abridged series there's a scene where Batman literally punches through a guy's windshield and demands "license and registration." After he causes the truck to crash he remarks "that's what you get for driving without a hubcap."

Western Animation

 * Despite the very low canon number of clones and several mentions in story of how tightly stretched they are, Star Wars: The Clone Wars has them doing everything from street patrol to prison guard duties.

Real Life

 * Can be Truth in Television on occasion in some parts of the world, often due to Values Dissonance; at one time it was quite common to see officers of the then-Royal Ulster Constabulary carrying sub-machine guns on routine foot patrols, for example, but at the height of The Troubles there was every likelihood they'd need them.