At At times I see bumper stickers and do not understand what I see. Take this one "Prayer Changes Things" - what things? it is a catchy phrase, but what is the context? Besides the obvious "I believe this statement", I find bumper stickers annoying and intrusive. I don't care what you believe, eat, wear, endorse, how many kids you have, or who is your copilot. I want you to get out of my way so I can get were I am going.
I have a camera with me all the time. When I see something odd, I shoot it. Take the NOTW sticker, it is a plug for Christian themed clothing. I've seen the stickers for a year without understanding what they mean. I was disappointed when I realized it was a commercial venture.
I recently moved my bumper sticker collection to Flickr. Check them out if you are interested.