It was still a thing when this permies thread was started in 2019:
https://permies.com/t/123310/Funny-bumper-car-stickers
I wrote back then, "I *really* want a bumper sticker for my bicycle that says, "My other vehicle is a back-hoe loader." Maybe I could make one that would fit on my pannier?"
I painted one up, but it faded out after a couple of years.
My biggest problem with bumper stickers is when the writing is too small and people tail gate to read it. I guess that's where the sticker came from that reads, "If you can Read this Bumper Sticker, you're Too Damn Close"!