How do you pronounce #winning aloud? Would it be hashtag winning, hash winning, pound winning, winning or something else? This goes for all hashtags.
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So #winning is "hashtag winning". To me, this makes sense because if you are saying it out loud people may not know you are referring to Twitter. Saying simply "hash [tag]" could be miscontrued because "hash" has more than one meaning.
I have always heard Twitter hash-tags spoken as "hash [tag]". My source being personal experience in British English.
Americans often call the '#' symbol the pound symbol in my experience, so this may well be valid too. Saying "hashtag [tag]" is often redundant and overly-verbose. That's my view at least.
Depending on the context, I'm going to go out on a limb here and say that it isn't typically meant to be pronounced, unless you have some good reason to draw attention to the fact that this particular term can be searched for.
It is pretty common in a tweet to just mix hashtags into a sentence like normal words, but with the meta-data (mostly useful for tools) that it can be searched on to find related things.
However, in conversation we don't have computerized search tools available (unless you work at the NSA), so there's no point in including the metadata. You should probably expand any abbreviations though, so the poor slob you are talking to has some idea what you are talking about.
For example, this tweet:
Would read out loud as: