I have not heard of it either, but I would not be surprised to hear it.
I knew a sheriff's deputy who would say things like "I parked my squad in front of the house."
Given the context, I was able to understand that it was his term for "squad car".
In a specialized occupation you develop specialized terms for the things you mention often.
What I call a "police car", some police call a "prowl car". From there to "prowlie" is not far.