I use these signs to remind myself and the kids that they have lost a privilege. These signs are a huge time saver, because once I put them up, my third graders know they aren't allowed to use whatever Privilege they lost. It also stops them from asking over and over when they can use the materials again, because they know once the sign comes off that they can use it again.
My third graders decided not to properly put away their indoor recess games for several days in a row. All I did was slap one of these signs on the drawer for those games and it's a reminder for them not only that they can't use those games, but they need to take care of their stuff.
Also works great because then substitutes know as well.