there’s no easy way to check if a Time Turner has been used other than to see if it can still be used
If the turner also has a restriction[1], it’s easy to check: just ask someone not important to try to use it. (Not important in the sense that it’s no big deal if they loose the ability to time-turn for a day).
[1:] It should have. They can be broken/destroyed, which suggests that they can also accumulate non-fatal damage (like scratches), which technically means that they also carry information to the past. But the information rules don’t seem to apply except when in some cases involving sentience.
If the turner also has a restriction[1], it’s easy to check: just ask someone not important to try to use it. (Not important in the sense that it’s no big deal if they loose the ability to time-turn for a day).
[1:] It should have. They can be broken/destroyed, which suggests that they can also accumulate non-fatal damage (like scratches), which technically means that they also carry information to the past. But the information rules don’t seem to apply except when in some cases involving sentience.