hwt8254 says: "THE FCC call sign for UOM PD"
The FCC dot gov site (database) should list the FCC station callsign.
If you are referring to an individual callsign, is it one that is assigned by the agency itself, U of M in this case? You would probably need to ask the agency itself for that info.
I hear (and log) State Patrol and County Deputies talking all day long using their three digit "agency" callsigns (311, 405, 943...). From the logging I have built my own database of radio ID's and associated "callsign", so I can pretty much tell who is where and when. And anyone on the ARMER system can turn-up on any and all sites. I routinely get to listen to calls from the Twin Cities area here in southern MN that come across the local tower and do not have anything to do my county.
Other than what I have presented, I am at a loss for anymore information that you are apparently looking for.