When you get a replacement pink hard hat - engrave your name somewhere inside it (if that isn't going to compromise the safe use of the hard hat) or use a permanent marker UNDER strapping or lining, so that it is hidden from casual view.
Then if a second pink hard hat goes missing - it can be proven that the particular hat was YOURS.
I had stuff that was marked with my name (in permanent marker) stolen when our company was moving from one building to another - I planned on packing MY desk at the last minute (Friday) and taking everything home to take back to the new desk (Monday). I came in one day to find some of my personal "organizing" stuff missing (plastic tray with several compartments, pen holder, and a couple of other things). I took everything home that day and most of it is still home, twelve years later.
The missing stuff never turned up - with or without my name on it.