The buildings of the Cambridge State Hospital had a few remnants of signage that I had never seen before. I heard them referred to as "Bliss symbols". My understanding was that the symbols were used as an additional way of communicating with clients who couldn't read. I most often saw them labeling sinks and bathrooms and other commonly used spaces.
I just recently heard an episode of WNYC's Radiolab that contained a segment about these symbols created by Charles Bliss. There is a much more complicated story behind them than I expected and they were created with much grander ambitions in mind. I thought it was a pretty interesting story.
The Radiolab segment is located at http://www.radiolab.org/story/257194-man-became-bliss/ . The segment about Charles Bliss begins at about 5:30 into the stream on the page.