Hard to believe, but
this guy actually collects do not disturb signs from hotels around the world. From his site:
Hotel collectibles have always been popular because people travel widely and enjoy carrying away souvenirs from where they lodge. However, most people take the more common items such as toiletry articles, stationery, matches, etc.
"Do Not Disturb" signs are often overlooked even though some are very attractive and original in design. I started collecting them quite by chance and it soon became an addicting hobby. Sadly, these signs may soon become a thing of the past as more and more hotels are replacing them with hi-tech electronic devices.