These tend to go for a lot of money these days, so some of these mid-20th century public information posters on eBay could be absolute bargains. Read more
The now departed BHS had some of these some time back, but not as interesting as the classic TfL information prints at Marks & Spencer. Read more
We're huge fans of this kind of artwork. In fact, we've bought a couple (for not a lot of cash) at auction in the past. If you also have a soft spot for public information posters, you might want to order Keep Britain Tidy: And Other Posters from the Nanny State by Hester Vaizey.