I meant :
ARAC - have the ability to 'Tag' and get cash for returning after the time limit and tow/ impounding
Police - would chose this option if the vehicle isn't in a dangerous place for RP
How about... You can only tow/ impound something that has been 'Tagged' (like one of those "This vehicle will be towed" signs) and stationary for 15-30mins?
The 'Tag' could be something that gets placed on or near the vehicle. Ideally a wheelclamp or a sticker... but could be a traffic cone...