Traffic cops are a trope that works in any form of game setting. Modern day, obviously. Future, sure - any time you have vehicles it's a given. Fantasy, not a problem - fantasy borrows many tropes from modern day life as it is (*cough*Terry Pratchett*cough*).

Historical can be a little more difficult. But if your Roman Empire campaign reads more like Gibbon than Goscinny & Uderzo, you're probably missing half the potential fun anyway.

Transcript

Trooper 1: You there, stop.
C-3PO: Jim, is this you?
Captain Antilles: {dead} Tempting... but no.
Trooper 1: We're looking for a dangerous lunatic and two droids. He's a home-schooled survivalist from a nearby off-the-grid compound. Have you seen anything unusual lately?
Luke: {small} Unusual? Noooo. Perfectly normal day. Status quo man, aaalllll morning.
Obi-Wan: So what does this lunatic look like?
Trooper 2: Well, he looks like... that kid there actually. Anyway, have you seen anyone by that description?
Obi-Wan: Besides this kid here that looks like him, no. No I haven't.
Trooper 1: That's a shame. We're all very concerned.
Obi-Wan: Luke, do you have a twin that you know of?
Luke: Huh? No, not that I know of.
Obi-Wan: Hmm. Well, you heard it from the kid himself. Sorry we couldn't be of more help.
Trooper 1: Say, kid, if you've got some spare time later, perhaps you could patrol with us and help give people an idea what this lunatic looks like. No insult intended.
C-3PO: Jim, are you sure this isn't you?