@simon I've always wondered if hashtags too were a semantic agreement born on Twitter, i cannot recall previous use on other platforms (beside for irc channels)

Now I've read https://en.wikipedia.org/wiki/Hashtag
and yes, we use only since 2007
https://twitter.com/chrismessina/status/223115412
https://stoweboyd.com/post/39877198249/hash-tags-twitter-groupings