Pesos de Paciencia (or Patience Dollars/Euros for international purposes)

In my last post I promised to share the idea I had after being dissatisfied with the service at a restaurant.
So here's what I thought of, as we were paying that last time:

The waiter brought the bill and we paid. When he brought back the change, we realized we had we had not enough coins or small bills to leave a tip. So we started searching frantically for any lost coin we could have in the hidden corners of our bags... as usual, D. had more coins than I did (I am a shame when it comes to paying, I sometimes don't even have enough money to pay for my food!). But with all our effort, we couldn't reach the 10% tip that we like to leave after a meal. I found a free postcard and said, jokingly, "I could leave them this, how much do you think it's worth?"
An then it came to me... the service had been quite disappointing, and what one usually does (at least over here in Bs As) is not leave a tip when you are not happy with it. We figured we would still leave the few coins that we could gather up, but we would also use the postcard as an opportunity to leave a little comment, or "constructive criticism", as I like to think of it.

So I started drawing something along the lines of a money bill on the white side of the postcard, and I decided that it could account for the amount of money I would have left as a tip, had I been happy with the service provided.
In other words, I thought that, as a creative way to suggest improvements, I could leave a personal money bill that is worth the tip that the waiter/waitress would have won had they not forgotten to take our order, bring our order and bring the check at the end of the already seemed like an eternal dinner.

D. felt a bit embarrassed by my idea, but I decided it was a pacific way to express my disappointment and not make a public scene (which usually makes everyone uncomfortable and upset). I hope I wasn't too offensive... what do you think?

ps: I will soon post a prototype of the bill, which I baptized "Peso de Paciencia" or "Patience Dollar"... anyone is free to use the idea if they find it suitable.