In Japan, I often spent a lot of time wandering big department stores like LOFT and Tokyu Hands, just looking at all the things for sale. While we have plenty of department stores here in Canada, none of them had the sort of novelty value of Tokyu Hands!
One thing that regularly caught my eye when shopping was the display of "B-Side Label" stickers at both of the above stores. B-Side is a brand of pop art stickers with a wide range of artists. Their stickers are often music-oriented, but I loved in particular the designs that took familiar things (like the Japanese highway sign above) and changed them. The "Warning" labels are also quite funny. This was a type of art humour that was much harder to find in Japan (I suppose since it was considered punkish or underground), and I loved looking through the racks of stickers whenever I visited LOFT or Tokyu Hands.
Many of B-Side Label's designs are written in English, so you can check out most of their designs at their online shop, right here.