I had not before encountered this form of protest. If I were living in a place with mandatory voting and anonymous ballots, I would almost surely write my name on the ballot to spoil it.

I do and I do. :)

I have never actually spoiled a ballot in a municipality-or-higher-level election (though voting for a list with hardly any chance whatsoever of passing the election threshold has a very similar effect), but in high school I did vote for Homer Simpson as a students' representative, and there were lots of similarly hilarious votes, including (IIRC) ones for God, Osama bin Laden, and Silvio Berlusconi.