If you think about a crown protector (or if you prefer: "guard") this one might come to mind:
Not sure if this is the most famous one, but it sure is one of Panerai's USP. More brands have thought of methods of their "own" to secure the crown, like Linde Werdelin:
Another one that came to...
I've had this one for around a year, worn a few times (although shows no signs of use), so it could be sold as BNIB. It's fitted with the ultra rare protector/bull bars which are probably worth as much as the watch itself!
I'm selling it for SOLD(for £60) delivered worldwide.
I'm looking to buy a G-Shock DW-5600 bezel protector (Casio part #74299032).
I may also be interested in buying a 5600 series watch if a bezel protector is included. I've attached a picture I found of a DW-5600 bezel protector on a DW5600E. Thanks for looking