There are only two identifiers on an ISP Mustang according to my research with ISP,
1. On the dash there was a Dymo label like in the eBay ISP Mustang photos:
2. The other is the license plate with an ISP 3 digit number which is a direct plate assignment for the trooper. Trooper takes the plate off and goes with him or her if they get assigned a different vehicle. As seen on one of the site photos:
So any of these cars have to have the property number on them for verification of service and who was assigned to the vehicle for now according to ISP as all their fleet records have been destroyed as have these labels since they are to be removed before auction. I, however, will not give up and will try to find another way for those without the labels.