You use something, odds are it will show having been used in some way. Conversely, not
using something for a while will make its disuse obvious. Car engines heat up; soup will go cold. When a detective or questioning character wants to know if a suspect has been in a given area, looking for Signs Of Recent Activity
can be a big tipoff as to whether their alibi holds true.
For objects it tends to be temperature, but people will usually show it as stains on clothing, dirty/clean hands, or the typically muddy shoes.
This is a basic skill for the Scarily Competent Tracker
- Encyclopedia Brown: a man claims to have just driven over. But while he's talking to the police his barefoot young son plays on the hood of the car and it doesn't burn his feet.
- Similarly in The Three Investigators' The Secret of Phantom Lake a man claims to have just pulled up during a downpour, but Jupiter Jones happens to put his hand on the hood of the man's car and noticed it wasn't hot. Then he looked under the car and it was dry, meaning that the man had been parked there for some time.