Plankowner is a term used by the United States Navy, and has consequently been variously defined by different units. The origin of the term is the implication that a crew member was around when the ship was being built and commissioned, and therefore has bragging rights to the "ownership" of one of the planks in the main deck.
Sailors who are plankowners at their current command often have the word "PLANKOWNER" embroidered on the back of their uniform ball cap to denote this designation. A plaque is placed aboard the ship with the crew names. When in port, the departure of a plankowner for the final time is usually announced on the 1MC public announcing system with a bell-ring, as <ding, ding> "Plankowner, departing".