Great structure here Street Art Cities - I’ve often wondered if there was a “code”, but have been doing it this way from the beginning, so it’s good to have that reassurance. A few days ago, I actually had an artist who was working on a piece - the ‘first time’ I’d seen this in action, and so I politely said hi, so not to distract him, and then asked him if I could take a photo. He replied, saying yes, but only the back of his head :). I liked the idea of offering a drink or something - but didn’t think of that at the time, but will add this to my pocket!