Was this unmarked vehicle ICE or police? How to know the difference?

I saw a black, unmarked van with it's sirens on today on my way into work in Charlotte, North Carolina. I've never seen police have vans so I thought maybe it was ICE, but then I thought that ICE vans didn't have lights/sirens. Which a quick google search told me was incorrect. Is there a way for me to know if they're police or ICE?