I presume, based on the pattern you've cited, that you are looking for the NYC Department of Environmental Protection Police numbering. If so...
# = Command (Location - "radio ID")
1 = 1st Precinct (Gilboa, "Schoharie" County, near Schoharie Reservior)
2 = 2nd PCT ("Beerston," Delaware County, near Cannonsville Reservior)
3 = 3rd PCT ("Downsville," Delaware County, near Pepacton Reservoir)
4 = 4th PCT (Olive, Ulster County, near "Ashokan" Reservior)
5 = 5th PCT ("Grahamsville," Sullivan County, near Rondout Reservoir)
6 = 6th PCT ("Croton" Yorktown Heights, Westchester County)
7 = 7th PCT ("Hillsview" Yonkers, Westchester County)
8 = Detective Bureau
9 = Special Operations Division
#W_ _ = PCT cars. #W1 = Commanding Officer.
W1 = Chief of Police, W2 = Assistant Chief of Police, W3 thru W5 = other executives (Captains). Be aware that these unit IDs are valid on only the DEP's own radio system. The counties that they operate within will often assign them IDs within their own county numbering system (i.e. 950s in Schoharie County and 7F### on DSP channels).
If you were looking for the ID system of the other elements of DEP (i.e. Hazardous Materials), I'll refer you over to pages 74 thru 76 of Edition 7 of Scanner Master's Metro NY / Northern NJ Communications Guide.
How about sharing the frequency you're hearing them on up there?