I have a book that shows wonderful examples of sailor's valentines. I had forgotten about them until you mentioned them.
Sailors' Valentines were brought home from a sailor's voyage at sea for his loved one during the early 1800s. They consisted of octagonal wooden boxes with intricate shell designs on them. The idea that sailors were able to make these on their ships is unlikely. Most "Sailors' Valentines" originated from the Barbados area, an important seaport during this period. Most historians believe the women on Barbados made the Valentines with local shells or shells brought to them from Indonesia, and sold them to the sailors.
Today, antique and reproduced "Sailor's Valentines" are sought for their beauty and uniqueness. Many Sailors' Valentines, both new and old can be found on the Island of Nantucket, Massachusetts.