Apart from statuatory notices (e.g. Traffic signs, etc) it has always been the law - in this country - that such notices had to state the authority under which it was issued to be legally enforceable. The 'No Fishing Permitted' sign has no such authority on it, e.g. Poole Harbour Master, and is thus not enforceable.
I caught a goby on bread trotting for mulletn once on holiday. Be good to get a wrasse although chasing mullet is too much of a draw for me. Those micro species are cool though