Why are you putting on the helmet? Would it not be more visible on a t-shirt or something..? You can put some funny comment on the t-shirt... saying something like :

"If you take photos of this body, you have to pay in Bitcoin"

"Photo tipping to this address ---> {insert Bitcoin address}"

Remember the QR Code are used for many other things too... the Bitcoin symbol should be bigger, if you going to draw attention to it.