It depends on the assignment. Tactical stuff has its own uniform, as does cellblock or prisoner transport. Court calls for a suit, and warrants is just street wear. In NYC, the accepted warrant uniform appears to be work boots, cargo pants, a tee shirt under a sports jersey, and some kind of baseball cap. Goatee is optional.
I was just in Philly for a week, and the uniform of the day was a suit and tie. First time in a while. I'd forgotten how little I like wearing them. I think I'll wear flip-flops and cargo shorts for the next week, just to get my equilibrium back.
"There is only one basic human right: the right to do as you damn well please. And with it comes the only basic human duty: the duty to take the consequences."
-P. J. O'Rourke