That's a merkin, not surname Merken. Surnames are a whole different ballgame which is why there is etymology and nomenclature etymology. Take surname Holiday - everyone knows what a holiday is don't they? But the surname came form 'holy day', nothing to do with the modern meaning of 'vacation'. And Mr. Holland. An amateur would assume his family came from Holland. But he would be English, from places in Esses, Lincolnshire, Lancashire where the name means 'land at a Hough', hough being a hill-spur.
The faux pudenda is nice trivia and certainly gives one some scope for teasing but it's not the etymology of the surname. And certainly not a sporran....though I thought the Scots joke was funny ;o)