Definition of "hashmark" [hash•mark]

• An insignia worn on the uniform to indicate years of service. (noun)

Gnu Collaboartive International Dictionary of English: licensed under The Code Project Open License (CPOL)

• "I was set with Online Improv Friday (OIF) until I learned what a "hashmark" is."
• "Though the words it calls out are mostly common, the use of the hashmark seems gratuitous, given the limited length of the medium (something that Stowe Boyd points out) and that the hashed words comprise the meat of the message, rather than the meta."
• "I proposed the hashmark (#) as a way of adding context to a tweet, so that people could choose for themselves to filter out or follow tweets tagged with certain keywords."