It means number, love
In texting, the # symbol (A.K.A. The number sign) usually occurs when the person texting is about to mention a number. This could be a phone number, ordered numbering from a list, or anything of the like.
For instance, person A may text person B, asking for age by saying "Hey how old r u in #", implying that A wants B to tell A the age in actual digits, instead of words (to be honest, this may not be a good example, as I don't text as frequently as some others do).
However, the # symbol is more commonly identified with Twitter and the hashtags used by users to tweet messages to their followers.
Usually in a hashtag, people put a phrase with no spaces and necessary capitalization (if it needs it). It's a pretty simple concept - I don't have a twitter, yet I know that this is pretty much how the # symbol works in hashtagging.