In the US, I think it varies by local ordinance and custom. I happen to know a little about Minneapolis because there was a lawsuit about busking a few years back which was covered in the newspapers. The city council had first passed an ordinance saying you had to get a license, and then refused to grant any licenses. One musician, who had been busking for years before the law was passed, and who had applied for a license and been turned down, sued the city and won. A judge ruled the city had to issue the license unless they could show cause why not. (I have no idea what kind of thing the judge would have accepted as a valid reason to refuse the license.) They issued the license, and I think the guy still plays to this day. He plays a conga drum and sings on Nicollet Mall in summer.