When addressing police or jail staff, a lot of times you address them as "[Rank] [Last Name]", such as "Sgt. Smith" or "Lt. Reynolds". If you don't know their rank though, you can resort to "Officer [Last Name]". (Again, I'm just referring to police and jail guards there, not military.)
What's the equivalent for firefighters? They have military-style ranks, but what if you don't know a firefighter's rank?