Are you looking to charge somebody with something or seeing how stiff the penalty will be if you want to take a souvenier?
I personally can't fathom why someone would need to steal a seatbelt from an operational aircraft as a souvenier, when they could relatively easily purchase one from a boneyard / chopshop, or eBay (and probably from a much cooler aircraft!).
I find it peculiar that tampering with smoke detectors falls under a FAR, but not tampering with other safety devices.
Any case, thanks for the responses.