I think the best enforcement would be that you get a warning and a free mask - the first time. Who you are gets entered in the system. The next time, if there is one, you get the fine.The problem I have with this is that I don't want to see people who are out working getting nailed for $500 for forgetting to wear a mask. This is a tough one to apply fairly.
Can you imagine the screaming and teeth nashing if a homeless guy got a ticket? Or one of those "one mom with 10 kids" folks?
Having the balls to come right out and say you aren't going to follow the law though - that deserves the most severe consequences the state can dish out to the Sheriffs. Those fuckers are supposed to protect and serve. Not endanger due to stupidity.