The intriguing shape shifting selkies are a rich part of Faroese, Icelandic, Irish, and Scottish lore.
A selkie is a creature who lives as a seal, but can assume human form by removing its seal skin. You can slap the myth onto a letter in stamp form too.
Selkie stories are generally romantic tragedies.
In the film The Secret of Roan Irish, a fisherman steals the selkie's pelt while she is sunbathing. She is then forced to return to his house, as she cannot escape back into the sea, and becomes his wife and bears him children.
He stashes away her skin and years later, one of the children finds it and asks what it is. The wife immediately drops what she's doing, retrieves the pelt from its hiding place, having long ago dispaired of ever finding it, and returns to her former life as a seal.