Our car has a Mary Kay bumper sticker on the rear window. My wife used to sell Mary Kay, but does so no longer. It's now brittle and flakes off around the edges; man, I wish I could just peel it off. I also get my fair share of flak at work for driving a minivan with a Mary Kay bumper sticker. I work for a cable company, so it's mainly young, arrogant, single guys.
But we
did, one time have a lady shout to us from her car at a McDonald's drive through if we sold Mary Kay. Our car also has a dealership sticker from Mount Vernon, IL, and she lived in Mount Vernon and was looking for a Mary Kay consultant. Unfortunately, we lived too far from Mount Vernon at the time for her liking.
I like having three (soon to be four) Mexican import sticker residues on my windshield. I feel like I belong to a secret club that only Mexicans know about. I can be sitting in a parking lot, see the same residue on someone else's car, and know that they travel to México; when they come out, I can ask them in Spanish where they've driven to. Maybe we need a secret handshake, too.

I'm a Christian, and I like Christian bumper stickers. But I also like bumper stickers that make fun of Christian bumper stickers. My two favorite Jesus-type bumper stickers:
(Serious) If you think you're perfect, try walking on water.
(Poking fun) I found Jesus/He was behind the sofa the whole time.
I'm not sure what to make of the 'In Loving Memory of...' rear window stickers. On the one hand, I like the memorial idea. On the other hand, am I expected to feel bad whenever I see it? Mixed feelings...