stick a notice on your drawer saying: "I know who you are. Your theft was witnessed and I have got evidence.
Seriously? Do you really think that people that have found £500 in a particular desk drawer are stupid enough to go back there to see what Post-It notes have been left in their honour?
Don't be so fucking soft, a thief doesn't return to the scene.
Besides which, if you had witnesses and evidence you wouldn't be leaving silly post it notes around the place bragging, you'd just have the cleaner nicked.
There are some fucking dullards on here at times. I'm not surprised that the OP thinks post-it notes are a good idea, seeing as he thinks that unlocked office drawers in high theft areas are good places to store 500 nicker.
Call me harsh, please do, but there are some fuck knuckles about.