Do the signs at your library include or exclude?
This was a sign at the blood bank. I have read The hitchhikers guide to the galaxy (a very long time ago), so I thought I knew the quote it was referring to. I may still work if you have not read/watched it (or at least I think it does), because the key point is how long blood lasts (or at least that is how I read it).
There is a however to this. Because I was taking a photograph in the interview room (you have to answer a lot of questions before you can donate blood, plasma or platelets), this started a discussion with the nurse who had not read the book, seen the film or television series. She was commenting on how excited another donor had been seeing the poster. This made me wonder if it was too niche. I think it works even if you don't know that that many of the words form a quote as the key point is blood lasts 42 days so there needs to be continuing donations. It highlights that there can be many ways to read a sign.