Smallville 8.12 "Bulletproof" spoiler- Clark as a cop
Smallville episode 8.12 "Bulletproof" 
Airdate: January 2009
Clark Kent goes undercover as a police officer when John Jones (aka Martian-Manhunter-turned-human) was shot. Police inspector Dan Turpin gets suspicious of Clark’s disguise when he finds him talking to the Green Arrow. A Dr. Emil Hamilton helps Clark and Oliver with John Jones’ unique physiology.
According to Kryptonsite, several characters appear in this episode as reference to either comics or Smallville-lore. The site also cautions that the presence/characters of Turpin or Hamilton may be changed as "cop sentiment over costumed heroes and vigilantes is rather low". I didn’ t know this, but it does make sense that police won’t like vigilantes. If you think about it, superheroes do take matters of law and order in their own hands.
I like good superheroes who take justice in their own hands. With the only condition they don’t hit innocent people or people who can’t protect themselves.