This is at the break room where Alan works. Perhaps they are trying to distinguish between the verb and the noun. Maybe nobody actually uses the sink, so it's not functional and therefore a "sink". In which case, those quotation marks seem... disrespectful.
I don't usually post the following: newspaper headlines, personal email, craigslist postings, unprofessional websites. I also tend to not crosspost things from other blogs, since I have so much unique material waiting for me to get to it.
Things I see a lot: silica gel "do not eat"; hair dryer labels; inside the bus "do not drill"; Wal-mart sign about IDs; coffee machine with "2" cup sizes; employees must "wash hands".