The ones we are talking about aren't bumper stickers, they go inside a window
(which is why it has lasted about 20 years), so the sticky side is the right
side. The UK doesn't seem to do much in the way of bumper stickers. I could
do a photo of it for you so you have an idea of what it looks
FWIW:
Check out cling sticker 'paper' where-ever you buy your specialty
computer paper.
I don't know that it would last 20 years, but it isn't expensive and
could be reprinted as required.
One could also be printed on paper and stuck into a sleeve that would
adhere with a sky hook (= suction