This is a pre-owned Rolex Oyster Sea-Dweller Anchor  made of silver. It was included with the purchase of a Rolex Oyster Sea-Dweller  watch.

The anchor is 1 3/4" long and 1 1/2" wide. Writing on the Anchor -  "Guaranteed depths of 4,000 FT. Underwater,... 1,220 Meters."

From the 1950's to 2005, anchors were a special  item included with a new Rolex watch, with a  chain attached. I cannot give a specific date for this anchor, but it is a recognizable and collectible symbol of Rolex.