Even here in the "Vanilla-Ville" Northern Chicago Suburbs I see AR's in Police Cars all the time, more so than even shotguns now a days.
I was visiting my Dad over in Northfield about a year ago, I drive right by the "back" of the police station on my way home. While waiting at a stopsign I watched an officer going on duty removing his AR from a bag and "checking it out" before putting it back in his trunk. BTW for those not familiar with this area Northfield is a small town of about 5000 people with about zero violent crimes per year. The PD consists of 21 officers but they only have about half as many cars. Most of what they do consists of Traffic stops and DV calls.
"....The swords of others will set you your limits".