Go for the "begger's permit." I was once busking with my guitar just after dusk and across the street was a guy who was just sitting on the sidewalk, asking every passerby for spare change. In between people, he was talking to himself, actually arguing with himself and screaming and cussing (he was just nuts), but then, when somebody came along, he'd straighten up and put out his hand. I was across the street singing and playing my heart out (not much traffic and quieter, better acoustics). He was raking in the dough and I hardly made a toonie. Go figure.
Giving people a reason to stop and give is very helpful (asking them ) or playing in a very engaging manner (well doesn't cut it on the street). Kids with violins tend to make a lot of money .... people want to help out, they're going somewhere or could use help with lessons. In Canada, busking in front of the liquor stores when it's raining really gets the sympathy coins rolling out .... etc, etc.
I'm not sure the mute is a good idea because the street can be loud and you need to be heard.