The club doesn't have to know but in this case I suspect that they did know.Im slightly disturbed about the fact that you Poles seems to think a 50ft banner of a Nazi soldier with a gun to the head of a child is all good at a football match. As I said already Im personally not too arsed about the slogan but it is still clearly against UEFA rules and in my opinion banners etc should stick to football and not politics/history/etc - do them about your rivals or celebrate your players or victories or whatever but all this stuff has no place at a football ground in my opinion.
Would the club have known about this in advance and okayed it?
or is this something the fans put together without knowledge of the club (in England the club have to pass any banner of that size)
In that case we should forbid all minutes of silence, PL players wearing poppies during Remembrance Day (disgusting) and ban all players who wear black armbands after tragedies.