"Nobby" is a traditional name for all "Clarks". I am a Clark. I was given the nick in 66 when I joined the navy. It's pretty much stuck. There are a few stories about the origin of the nick, none of which have ever been confirmed, but apparently it started in the UK WAY back in the days of sail. Evidently it's an old Royal Navy traditional nick.
In my youth, I also had knobby knees, which is of course, of no consequence at all.