It's the single tear on the Wal-Mart smiley face that really sells it.
ETA: One protest group, though not, sadly, the same one as the link above, has called off their protest. Why, you ask? The recap goes something like this:
Potential protester: Wal-Mart supports gay marriage! And mandatory buttsecks! And is the Devil!
Wal-Mart: Wal-Mart "will not make corporate contributions to support or oppose highly controversial issues unless they directly relate to our ability to serve our customers." Translation: We intend to keep doing exactly what we were doing, which by the way never had anything to do with gay marriage in the first place, you morons.