The #hashtag or # plus a name, appears anywhere in a tweet that you want to add to a public list with that title. Like #truthseeker.
It can take the form of a running joke, often with Conservatives being the butt, or it can be somebody you support like #StandingWithWomenOfTexas or #WendyDavis.
The popular ones in the past 24 hours have revolved around Texas State Brown Shirts confiscating feminine hygiene products and such from women entering the State Senate Chambers, although guns are permitted (I am not making this up).
So I've been adding to the 'tampon' hash tags (when I can come up with one), but there are hundreds of great ones.
PS About real Luddites: they weren't entirely wrong and are mostly misrepresented in their actual beliefs.