I like the idea of bumper stickers, keep them simple and easy to read - website addy and a basic description of what it's about, eg healthy tasty treats for your dogs/pets. or what you have in your siggy, All Natural and Preservative Free Treats.
Straight and to the point, pet owners who spot it will go Oooh that sounds good!
If I see a bumper sticker, I look at the website addy and sometime have NO idea what it means - and often there is a vague slogan, I immediately lose interest, but when I've seen one that I can clearly understand what is being advertised I've often remembered the addy and looked it up.
Hehe, I'm placing an order soon too, just can't decide what to order!