Stopped Clock

A useful method of telling when a certain disaster/event happened is that all of the clocks have stopped at the same time. This can also happen to individual time pieces that have been damaged.

Power cuts can be neatly illustrated with a digital clock flashing '12:00' or '00:00'.

Examples of Stopped Clock include:

Film

In Pan's Labyrinth, at one point it is implied that Captain Vidal's pocketwatch originally belonged to his father, which the latter broke at the time of his death so it would freeze at that time in order to show his son "How a brave man dies" and later Vidal had it repaired out of spite. As Vidal is about to be killed by the rebels he takes out his watch presumably to break it again and asks that his son be told the time of his death only for Mercedes to cut him off to say "He won't even know [his] name" followed by her brother shooting him.
The clock tower in Back to The Future stopped after being stuck by lightning, giving Marty and Doc a precise time to use the lightning to time travel.
The War of the Worlds (1953). After the Martians use their heat ray for the first time, all the watches of the people in the nearest time stop. When this happens, the people notice that all of the watches stopped at the same time.
In Chinatown, Jack places a watch under the car of the person he's tailing. That way he could know at what time he left by the time the watch was run over.

Literature

The Quiet Earth. When John Hobson wakes up he finds that his watch has stopped at 6:12. As he explores the deserted world he finds that all watches and clocks have also stopped at 6:12.
Agatha Christie used it, of course. In "At the Crossroads", it's one of the stock detective-story elements faked by the Genre Savvy murderer to make himself look innocent.
In Great Expectations, Miss Havisham's clocks are all stopped at 8:40—the exact moment her groom-to-be jilted her.

Live-Action TV

A stopped watch used to be a common method of discerning time of death when the cause of death was a fall from a great height. This was abused in at least one episode of Midsomer Murders to make a murder look like a suicide.
A minor plot point in Ashes to Ashes. Whenever Drake asks Keats for the time, he gives her the same time: the minute Drake died.
One episode of Columbo involved the time of death being established by a broken watch. Columbo figured the watch must have been planted on the victim's body with the time pre-set, because he was a tough sportsman who wouldn't have wanted to be seen dead wearing such a wimpy, fragile timepiece.
At the end of the multi-part episode of Lois and Clark that involved Clark being lost in time, the exact time of his departure is needed to save him. Good thing said departure involved an explosion that damaged the Big Bad's watch.
The Twilight Zone episode "Where is Everybody?" depicts a man wandering in an empty town. In one building, he finds a broken clock. The implication is that the clock must have stopped at whatever time disaster struck, scattering the inhabitants. We later learn that he broke the clock himself in his attempt to escape a space simulation chamber.
In the Doctor Who episode "The Wedding of River Song", every single clock on earth is stopped at 5:02pm on April 22, 2011, because time itself is broken by River refusing to kill the Doctor, which was a fixed point in time.
In Once Upon a Time, the clock in Storybrooke is not working, which is to indicate that time is frozen. When Emma arrives in Storybrooke, the clock starts working again.

Newspaper Comics

There's a The Far Side cartoon where police are investigating a shooting at a clock store. The place has been shot to pieces, all clocks are reading the same time as each other, and the detective is wondering "Now if only we could determine the time of death...."

Video Games

In FEAR 2 all clocks have stopped after the events in FEAR.(Bonus points if you can tell me the time)
In Dead Space 2 all the clocks have stopped (permanently) at 12:00, odd, considering they are powered L.E.D clocks that would normally keep going, or at least flash.
Fallout 3 has every single clock you see stopped at the exact time the Chinese attack occurred. Seems like some of them would have been wind-up or something...
The Ace Attorney series use this idea many times - twice in the first game alone.
In Silent Hill Homecoming, all the clocks in town are stopped at 2:06.
In the Agatha Christie pastiche Interactive Fiction game Death Off the Cuff, the victim's watch stopped at the time that he was stabbed. Except that, much like in the actual Christie example, it was faked to draw suspicion away from the perpetrator of said stabbing.
In the adventure game Gray Matter, strange and seemingly supernatural events happen around the Oxford University campus, and each time the clock stops at the time of the event.

Web Animation

Homestar Runner: In the Strong Bad Email "vacation", Strong Bad sends a postcard from (among several other places) "It's that CLOCK (Look at it go!)". Of course, the clock isn't going at all.

Strong Bad: Okay, the best thing about this postcard is if you look at the clock, that's the exact same time that I first laid eyes on the clock! 2:55, man. And like, iddi—oh, wait, it still says... 2:55. Okay, well, the clock is broken, but still! It's about the best thing I've ever seen [sings] in my whole liiiiiife!

Western Animation

Johnny Bravo: Subverted in the episode "The Day the World Didn't Move Around Very Much". A jet cutting a power line stops Johnny's clock at 12:00, and after seeing similar events, he's convinced that time has stopped for everyone but him when in fact he runs into various instances of things intentionally standing still for other reasons.

Real Life

The Hiroshima Peace Memorial features a clock whose hands have stopped at the time the A-bomb was dropped, 8:15.
- A similar monument in Japan actually depicts what time the Kobe earthquake struck.
Mormons refer to Joseph Smith's time of death by what was on his watch when he hit the ground after being shot out of a prison window.