I read this sign every year. Let me type it out for your edification: "[Kapok] is found inside some life jackets, during WW II [World War II for you youngsters] they were known as Mae Wests, because the fiber is light-weight and waterproof." Now I won't dispute that the petite Mae West was light-weight, and she may well have been waterproof; however, this is not why the kapok-filled life jackets were called Mae Wests. A friend pointed out to me that the parenthetical clause between the commas was just out of place and should be deleted: "[kapok] is found inside some life jackets during WW II because the fiber [not Mae West] is light-weight and waterproof."
If you don't know why the life jackets were called Mae Wests, you're too young to know.