YSK that if your turn signal is blinking unusually fast (like 3 or more times a second), it generally means you have a bulb out.
Why YSK: Your signals alert other drivers as to what you're doing; a signal bulb costs a few bucks and is usually a quick and easy repair to do yourself (consult YouTube); and any place that regulates motor vehicles probably requires you to have working turn signals. So knowing when and how to replace a burned out signal bulb can save you an interaction with law enforcement.
Adding: You can diagnose which bulb is out by turning on your hazard lights and checking all four corners of your car. It'll be the one not flashing.
This is also probably a good time to check your brake lights. Put something heavy on the pedal or have a friend hold it down and check that all three brake lights illuminate. Replacing a burned out brake light is also usually pretty cheap, quick, and easy.
Here's the EVERY FUCKING ONE. Seriously what's wrong with you people? It's bad enough that cars in the US aren't forced to use amber turn signals, but I guess it doesn't matter here because no one ever touches the damn blinkers!
I can't speak for everywhere, but in Brazil the emitted light must be amber by law. Some after market parts and some auto makers get creative and manage to put a red mask on it that somehow still lets amber light through. But it's rare.
Except when they're already merging in front of you. It's like thanks bud, glad you thought to use the signal when two of your wheels were already over the line cutting me off. Cool cool cool.
I am willing to cut some slack in a "oh shit, forgot the blinker this one time!" spirit. But yeah, using means using it properly. Enough in advance that other cars can react and don't forget the fucking thing on forever. How do people not get annoyed by the clicks?