It's an emphatic exclamation. As you well know, it's just a contraction (corruption?) of Isn't it? serving in a rhetorical sense, not really a question but a statement of confirmation. I have a related question for you: I have sometimes heard the grammatical subject of the sentence repeated at the end of a sentence, in object form, for what appears to be the same reason, as a kind of emphasis. Examples (and please forgive incorrect execution): I like Marmite, me. We're going down the pub, us. My question is regards usage. Is this a regional use, found some places and not in others? Is it a generational thing used by people of a certain age? Is it a register thing indicative of level of education? Or is it just something some people do, like up-talking? ... etc.?