Which is every bit as definitive and authoritative as any Wikipedia article.

Ah, yes, I had forgotten what low esteem the Wikipedia is held in in these quarters. I am sorry, please excuse the laziness on my part. If it's any consolation, the article linked to was just to give one an idea of who Guizot was. The quotation is not mentioned in the article, but googling Francois Guizot turns up plenty of attributions of the little folk meme in question. If I am not mistaken G B Shaw remained a socialist into late life, and, so, the statement seems out of character, though, I suppose he could've meant it ironically.

Ceci n'est pas un seing.