Trolls on the forum 4chan are trying to turn the hashtag into a symbol of white supremacy.
A post to the /pol/ message board from an anonymous member calls for others to create propaganda using the pound sign.
"We must start using # to represent the swastika on memes and social media," they write.
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"It will be a perfect win-win situation. Either Twitter will have to accept blatant Nazism on its forums or it will effectively have to find a way to get rid of the site's core mechanics."
The movement, dubbed "bashthehash", has already taken off. A search of the tag on Twitter shows hundreds of posts which associate the hashtag with Nazis and the far-right.
4chan has pulled off similar campaigns in the past.
In 2017, the forum convinced so many people the "okay" hand symbol was linked to white supremacy the Anti-Defamation League released a statement calling for people to consider the context the symbol was used in.