This tendency for parents to bask in the reflected glory of their children is a little disturbing. Being proud of your children is great...justifiable, even. But to shout it from the bumpers of your minivan seems to be counterproductive.
This silliness, of course, spawned a host of parodies, mostly mocking parents who think that someone will see their bumper sticker, pull up along side them, honk, roll down their window and shout, "Hey, you must be an exceptional parent to have such an intelligent child! My heartiest congratulations!"
The first parodies to appear seem to be the ones from dog lovers / dog owners. As cute as this was (for about a week or two), it's now tiresome. First of all, the smartest dog in the world is dummer than the dummest student. I hate to say it, but it's true. Dogs are a lot of things, but they're not wired for standardized testing. They are, compared to honor students, dumb as a bag of hammers.
Now it seems like being an honor student is a bit of a pariah. Maybe it's because our society likes people to fail, as it makes the average individual feel better about themselves (cif. Festinger's theories of Social Comparison). I dunno.
So while I think it's silly to put a bumper sticker on your car with your child's IQ on it, I think it's almost as silly to parody it. That said, here are some hat I found that I like very much, my favorite being the one I found at Sundance last summer (the chihuahua one).