There is a dusting you can do that will show up finger prints on the inside or back side of the instument cluster. I don't remember the chemicals name but you either put it on like the police would or use comprressed air and spray it so at least some gets behind the cover. Then turn on your black light and see the finger prints show up.
There are plenty of valid reasons why body oils can be found on instrument clusters, so to be sure you don't accuse someone of the wrong thing you need to make sure the actual numbers on the odometer glow from the test. Even then its no garauntee, but should be a good way to look out for possible tampering.