There is no transmitter located in Nassau, the nearest one is in Queens right on the border at Creedmoor Psych Center.
The system was never properly assigned to Nassau and Westchester counties for some reason, even though there are talkgroups active in those two counties. I fixed that.
MTA PD is using the Metro 21 in Staten Island at the bus terminal, and soon in other places too. Could be them, but I havn't bothered to listen since we are not maintaining the system, yet, if ever at all.