What do you do when you have a some neon yellow Post-it Notes, a Sharpie, some free time and access to a fire alarm? Why play a prank of course.
Of course, a prank like this is probably against dozens of building and fire codes, but it is amusing none the less. Of course, no adult would ever actually confuse a fire alarm with a candy dispenser, but it wouldn't stop some buzz-kill from removing the post-its.
If you want to go for a real fire warning prank that is generally harmless, go and buy a half dozen or so Fire Extinguisher signs and mount them around your office (preferably with a permanent adhesive) pointing to places and things that are obviously not Fire Extinguishers. Point at a plant. Point at a computer. Put it above a table where it can point at a glass (half full) of water. The possibilities are endless and endlessly infuriating for any building manager. When you can buy a Fire Extinguisher sign for three dollars, why not go hog wild?