If a cop doesn't have a mustache, he's a rookie. There are no known exceptions to this rule. Cops are their own gang, and the cop stache is the "gang tattoo" they use. Independent style requires independent thought, and those with independent thought would never become a cop. The cop stache is an inevitability for any aspiring cop.
Police Chief: "You're no longer a rookie, Johnson. Grow a cop stache or get out of my jurisdiction."
What happens when a man of age shaves off all facial hair but that above the upper lip, to create a more mature "cop" look. Prone to leaving onlookers slightly embarassed. Is extremely tacky (or, hidious). The cop 'stache should not be worn for more than 30 minutes.
"Woah, did you see that new cop 'stache he's rocking?"
"Yeah, but it kind of made me feel like crying on the inside"