This gave me an idea. We have fare collectors in SF, too, and some of them are in fact quite large, and armed. The fines for fare evasion are steep: upwards of $100. Of course, most people don't pay them, since it's just like a traffic ticket, except without a vehicle they can boot.
I have a better system: public shaming, with clowns.
That's right: CLOWNS.

If you don't have a valid ticket, the fare collector sends in the clowns (or clown, or mime), who then PUBLICLY MOCKS you on the train to the other passengers. "Hey, THIS GUY here is riding free! That means ALL OF YOU paid for his ride! Let's give the freeloader a big hand, everybody!" (honks nose)
There are all kinds of benefits: free entertainment on MUNI, employment opportunities for clowns (because underemployed clowns generally turn to prostitution, and that's just disturbing.)
I'd bet fare collections would go through the roof. Nobody likes a public shaming. This is something we abandoned with the stocks, back in Puritan days, and I think it was a grievous mistake.
If the city is afraid of losing revenue from fines, well, they can collect it on the spot: "$100 cash, right now, or I send in the CLOWNS, pal."
I think this is a fabulous idea, and I plan to write to my supervisor, Bevan Dufty, right now to promote it.
If you agree, and you're an SF resident, please do the same!