C.E. Evans wrote:
But the set up (which is my point) is the same way, including having different insignia--and in some department, different duty uniforms as well--for those with the rank of lieutenant and up. They're all referred to as police officers regardless if they are a corporal or a colonel.
But the set up is not the same. Starfleet has personnel who are categorized as "officers" and others who are not. Police agencies don't, they are all "police officers" because they are all peace officers.