It's a dual-edge situation: they do disguise better to ensure longevity, but that also might be a crux because they blend in so well it appears to just be an ordinary advisory sign.

Perhaps a '₿' symbol could be added, or the QR label size increased? 

Additionally, if you're considering revamping an existing sticker, try replicating similar design aspects of the 'GOT INFLATION' one (repeat a successful action).