Do you know by any chance if it was just a local campaign or a national? They have nice ideas for advertising their services there.
It's only in Zurich, but they have at least two trams painted like that judging from their clips as they run on different lines.
But it doesn't come cheap, 150k euros for one tram for 3 months..
Very few governments support such a kind of promotion on public transport.
Here in Europe, you can advertise almost everything on the buses or on tramways.
From Condoms and UberFood to politicians and cough..cough...Onecoin..