You could do some signals analysis, figure out what bluetooth devices and wifi networks tends to show up when ICE vehicles are close by, and use that info to track them.

I mean, both BT and WiFi will broadcast pings, start collecting data and use it against them.

Then if you have more advanced radio monitoring equipment you can probably find the radio frequencies their communications equipment use and track that.

I remember seeing a video about a police detector you could buy for your car, it listened for signals on specific police frequencies and since there is so much equipment that keeps a constant data link in the background it worked brilliantly, easily detecting every police car even civilian cars.

Remember, you can still use signals analysis even if the signal is encrypted.