My friends and I are official buskers in our local Farmers' Market. We have one of those charity buckets with a slot that people post money through - we hope! We know that we are not allowed to shake the bucket (constitutes "aggressive begging") but found that the income went up substantially when we put the bucket up on a chair and a wee bit further out front - so that people couldn't quite so easily miss it. At ground level it was easily ignored. We supplement this with flyers and leaflets for the music registered charity we are supporting. We have not, as yet, had any security problems.