Just tell people the reason why its a bad idea and why its illegal! If you catch some doing this, you report them to Fish & Wildlife (DNR)

Also there are for subspecies of painted turtle, Chrysemys picta and they are not all native to the same area. They are all distinctly different too.
western, C. p. belli
eastern, C. p. picta
southern, C. p. dorsalis
midland, C. p. marginata