technically you just stick the bitcoin logo on your guitar, and people will understand seeing the logo, so you indirectly promote bitcoin,
but for the problem of bitcoin starting to move away from ordinary people I think these ordinary people need space to understand how bitcoin works in the trading market you can see from the price of 60k $ to 38k $ this for new individuals in crypto makes scary
ordinary people who are new to bitcoin will indeed feel bitcoin is no longer good when they see the highest price at $60k and then drop to the $36k area, this is a very drastic decline. Ordinary people are afraid to enter and only people who understand can take advantage of the current situation.
back on the topic of promoting bitcoin by busking, it's actually a good idea and there are many other ideas that can be used, one of which is sticking the bitcoin logo on the guitar, of course, it has told the audience about bitcoin.