I've had this idea written down forever and only just decided to do it. Goes to show I really need to take action sooner. Earlier this week I created a sign that says "Please Interrupt Me" with a smiley face below it. I can't even count the number of times someone has walked up to me and prefaced their question with "I'm sorry to interrupt you...."
I've had so many positive comments - more from staff than students, because it's Summer and there are few students here, but still. Someone walked in and said something to the effect of "Wow, that's something you don't see very often!" Others have said "Wow, I really like your sign!" And in general, I just notice people glancing at it as the walk in or walk by.
Just a little thing, only took a minute, but it is catching people's attention.