The Reverend and Catalyst have both been posting interesting old signs over the last few days, so I thought I'd put this one up. I bought it at a book fair a few years ago, and the moment I saw it I knew I had to have it. We actually lived just a few blocks from Harvard at the time, and kept it on the wall in the living room. Now it sits on a bookshelf in my office. I've no idea when it was printed, but my guess would be the 1920s.
So remember- Don't be dirty! Don't be dirty! Don't be dirty!