Do you know by any chance if it was just a local campaign or a national?
I'm pretty sure Zurich and Geneva are the 2 biggest cities in Switzerland anyway. Even if it's just Zurich, that's pretty good exposure, there must be 10's of millions of tourists and other foreigners passing through Zurich every year, many of whom using the trams.
Very few governments support such a kind of promotion on public transport. Though Switzerland is technology adaptive, and has got its own cryptocurrency giving exposure to bitcoin on the main cities grabs good attention from tourists and foreigners travelling to Switzerland. Such a level of promotion need to happen at least on half of the world countries.