isn't that illegal is some countries? also that would create a legit reason for banks to go against bitcoin (IMO).
better not do that.
Its illegal in the UK to deface the queens money lol but tbh everyone does it and i cant remember a case of anyone being punished. Remember max keiser burning a £20 on live TV?
To OP you might aswell just write bitcoin on money as an advert.
Done this many times, no one says a thing.
Still spendable.