That is REALLY stretching it, I am quite sure every person seeing that sign knows it refers to somewhere you can get cruises on the Loch.
To me, that is just so completely obvious, I never even considered they might be stretching it that way for a joke.
Oh FFS, it's a joke. A bit of a laugh. Doesn't need a bleedin' thesis.
If you get it, fine. If you don't, move on.
If it really isn't funny then ignore the poster.
Be careful not to try and ignore yourself.