A couple of things.
Let's try to avoid words like 'Yanks Out!', Cancer, Apartheid references, references to other sensitive topics seeing the global scale of this. Let's also avoid words like c*nt and Fuck. Also, I am of the opinion that a simple banner would be more effective than a flashy one.
My personal suggestion was - Save our Beautiful Game - Gillett and Hicks Out!
The reason I incorporated 'Beautiful Game' was because seeing the global stage we are displaying this banner on, it will appeal to more people rather than a 'Save Liverpool' banner which may not interest global audiences. If we say 'Our Beautiful Game' instead of 'Liverpool FC' people may be more likely to go back home and Google who G&H are and exactly why they are threatening their Beautiful Game.
The problem with this is we do need to have a link to Liverpool though and so maybe we can put a Liverbird on the banner. Or maybe just a LFC in bold, red letters.
Just my 2 cents.