What are the symptoms of a bad timing belt?

Timing belts are made of a composite rubber structure and nylon reinforcement cords to provide longer belt life.
The car timing belt keeps all the internal moving parts of the engine in sync. It sometimes also powers the water pump, oil pump, and injection pump.
It is usually located behind a protective plastic cover on the front of the engine.
Symptoms of a bad timing belt include:
Burning smell from the engine
Rough engine idle
Engine misfires
Engine smoke
Rattling noises from the engine compartment
Drop in oil pressure
Broken pistons or valves