Fantastic idea, Rosemary!
Let's also add buttons that show the danger to our entire earth, caused by raising those poor creatures that are eaten: we could have pictures of forests dying due to climate warming - caused firstly from clearing for animal production, secondly from polution from animal production.
Then how about pictures of dead and dying fish, streams, rivers and oceans from the greed of over-fishing and once again, humans' polution.
More buttons could show ugly pictures of diseases caused by eating meat - if cigarette packages can come with nasty warnings, why can't our buttons show diseased livers, stomachs, etc., to add punch to our own campaign? We could get laws passed that mandate stickers be placed on every package of meat sold - 'caution, this product is dangerous to your health and the health of your planet'.
Wow - some advertising company could make a mint with this idea! AAS will be the next Ralph Nader of vegan-ism. Well, we can dream, can't we?