They’re on utility poles, newspaper vending boxes, traffic signs, all sorts of places.
If you tried to peel one off, you would destroy it. So photographing them is the only way to collect them.
This is the biggest one I’ve seen, life size. Technically not a sticker, a ‘wheat paste’ I believe they’re called. You can find a few pieces on ‘flickr’ also. I wonder if Pobresito’s work will show up in galleries some day.