Comment by int_19h

I don't know if there's any liability for doing that, but some of those car owners occasionally find out that their car was seized by the cops to "investigate". This might depend on state law, too. E.g. in New York:

"Members of the state police, any local police department or any peace officer acting pursuant to his special duties shall seize and confiscate a motor vehicle or trailer if any original identification number or special identification number is destroyed, removed, altered, defaced or so covered as to be effectually concealed."