Is it fair to punish absent students with a one-question exam?
I think that this is unprofessional, and is leaving the institution open to all sorts of action (up to and including legal proceedings, if it impacts on a student's progression, for example). For example, what if a student is unavoidably absent? 

If it's only "worth a point or two", then I don't think it's worth antagonising people in this way. The sarcastic note left on the door simply underlines how poorly thought-out this whole thing was...