Write messages on your dollars! This adds to their value!
Hmm. I forsee a new advertising medium ...
And then we can have a MoneyGoogle. If every dollar can have a semantic association, then googling for them would show whose money is where whose mouth is ...
What if it's a revolutionary and inspirational message, written in gorgeous calligraphy, so that I don't want to trade it? $1, keep it, no worries. But $50? Keep that and you've just sapped the currency, pal.
Would beggars finally start asking for words of advice?