Missing Coffee Mug!
Please help, I had my cup in the strainer on (insert date) and it has gone missing.
It was a gift from my daughter (or "loved one" if you prefer) and I would appreciate it's return. If the borrower would please return it here (the break room) it would be greatly appreciated!
You don't have to put your name on it, that way nobody feels like a theif when they see you.
Also, I don't know what kind of office you work in (ones I've worked in had 500+ employees), but I wouldn't bring something so dear to me to the office unless it never left my sight.
Good luck! I've had similar situations, though not something so special to me, and the item was never mentioned or returned, I hope you are luckier with this!