So where were these posters found? Somewhere in the city or at the venue?
If it's just somewhere in the city centre I can do some poster-spotting in Antwerp, Belgium tomorrow by walking to uni instead of taking the underground tram. It seems to be a stadium tour though, so in Belgium that would be Brussels and not Antwerp.
Edit: it's going to be rainy tomorrow morning. Might as well just take the tram and wait until the tour is announced. Stupid Belgian climate.