<P> Jimmy Fallon and Justin Timberlake performed a sketch parodying the often incorrect and misunderstood use of hashtags on Late Night with Jimmy Fallon in September 2013 . </P> <P> Hashtags are mostly used in unmoderated, ad hoc discussion forums; any combination of characters led by a hash symbol is a hashtag, and any hashtag, if promoted by enough individuals, can "trend" and attract more individual users to discussion . On Twitter, when a hashtag becomes extremely popular, it will appear in the "Trending Topics" area of a user's homepage . The trending topics can be organized by geographic area or by all of Twitter . Hashtags are neither registered nor controlled by any one user or group of users . They cannot be "retired" from public usage, meaning that any given hashtag can theoretically be used in perpetuity . They do not contain any set definitions, meaning that a single hashtag can be used for any number of purposes, as chosen by the creators of them . </P> <P> Hashtags intended for discussion of a particular event tend to use an obscure wording to avoid being caught up with generic conversations on similar subjects, such as a cake festival using #cakefestival rather than simply #cake . However, this can also make it difficult for topics to become "trending topics" because people often use different spelling or words to refer to the same topic . In order for topics to trend, there has to be a consensus, whether silent or stated, that the hashtag refers to that specific topic . </P> <P> Hashtags also function as beacons in order for users to find and "follow" (subscribe) or "list" (organize into public contact lists) other users of similar interest . </P>

When did the pound sign become a hashtag