Question is could it be classed as a death threat?
I'm personally not OK with a banner that depicts the decapitation of an opposition player even if it is by an over-milked 80s slasher franchise villain but that's just me.
Strange how apparently there are no rules (in Belgium anyway) about a banner depicting the murder of a player but a banner that mocks a players race, colour or creed or dares to suggest FIFA & Co are criminals.....