Could be. Last time I heard it was probably late 90s. It sounded like a rolling code inversion. Same stuff turned up on CIS. I assumed it was all state radio gear of some sort. I'd imagine they use DES or some other flavor of encryption by now. DCI traffic really got scarce once cellphones became standard equipment. All of the hunting down of sooper seekrit surveillance channels while not pointless, didn't provide the results it once did. Purple, CIS or otherwise.
Before I left the state I never did manage to pin down an identity of a channel ORANGE which I had heard referred to by a DCI agent while on PURPLE. Always bothered me as a monitoring challenge left undone I guess.