This fine weather vane is, I've since found, on the magistrates court's rear, riverside end. Clearly, despite looking like a common cormorant or shag, it's an attempt at the that old, medieval pelican in its piety motif that runs through King's Lynn.
Doing the minimal amount of due diligence that I always do for this work I find that the ancient slang term "Beak" meaning a magistrate has an uncertain etymology (maybe Dutch, maybe Saxon beag a gold collar, maybe this, maybe that ...) and is, in fact somewhat dated and out of fashion, being used only by old folk (like me) and limited to the London area. It seems "Stipe" as in stipendiary magistrate is very much the mot juste among the classes that need a word for a magistrate. Well, all I can say is that I've never heard anyone say "Stipe" in my 63 years but then I've led such a sheltered life.