Most buskers in Europe are from foreign lands far away. We all travel as tourists as it's part of the lifestyle. If we all sat around wondering if we're going to get busted, there wouldn't be any busking.
Buskers don't require work permits as everyone knows the busker is working off the books. You won't be illegal because you're travelling as a tourist. You will be subject, however, to fines and confiscation so do your research first and simply ring the police up and ask.
Look at it as an adventure...and I'll see you in jail
