Nicola don't make them too big or the vet will not kepp them up..A4 is a good size...make sure you put a pic of a really cute bun to get attention....then as few details as possible..people tend not to read huge amounts on posters.
Just name of rescue and tel number..the fact it takes in and rehomes rabbits...include "Donations Always Welcome" !! and of course.."Lots of gorgeous rabbits always waiting for someone special to take them home".......or similar..
sorry not very clear but typing this before rush off to vets! :shock: