These all came from:
  http://blogs.westword.com/latestword/2011/09/bizarre_classroom_posters_70s.php
  - they called it "Bizarre classroom posters" but I kinda like
  them. Now, we see posted like "Curious can be fun!" - and we've
  been trained to put an odd spin on "curious" - but really, think
  about it: curiousity is interest in learning - what's wrong with
  teaching that message? It show... "