I would go inside and demand to speak to the manager. If they are going to keep that sign up, I'd ask if they are willing to have flyers educating people on the care of these creatures, including info from the House Rabbit Society, etc., and from the local Humane Society so people know where to bring these pets when they are "no longer cute" - chicks and duckling definitely go through an awkward stage, or when the kids "get tired of them," and if the store will make a donation to the Humane Society.

That's just me.