The Sith have a new symbol in Star Wars canon, which seems to replace the one previously used in Legends. While Darth Vader and Emperor Palpatine were the two Sith Lords in the original Star Wars trilogy, it wasn't until the prequels released that Lucasfilm dove deep into the history of the Sith in canon. Up until then, practically everything Star Wars fans knew about the Sith came from the Expanded Universe (later Legends). But that's slowly starting to change.
It seems the Sith are returning to play a part in J.J. Abrams' Star Wars: The Rise of Skywalker, which is why, leading up to the sequel's release in December 2019, Lucasfilm is making a big push with more Sith-related content. They began with Palpatine's return being confirmed at Star Wars Celebration, and then continued with an announcement shortly before San Diego Comic-Con that Sith troopers will appear in The Rise of Skywalker. And now, it looks like another bit of Sith lore has found its way online.
Gearing up for Star Wars: The Rise of Skywalker's big Force Friday event, the merchandising team at Lucasfilm unveiled a batch of clothing and other Star Wars-related goods on the official Star Wars website, including a phone case that featured a new symbol with the word "Sith" under it (which has since been removed, but there are other Sith-related items with the same symbol still up). It would be fair to link the two together by association, but this particular symbol previously appeared alongside Darth Vader in Star Wars: Who's Who in the Galaxy: Character Storybook.
In that July 2019 book by Ella Patrick, there's a section that lists the Jedi and Sith in Star Wars canon, and to identify their allegiance, there's a symbol to represent both orders of the Force. While the Jedi symbol is one that's been around for several years, the Sith symbol was new - and it wasn't until now that it could be confirmed, without a doubt, that it's the new symbol to represent the dark side Force users in canon (at least ones that follow the Sith Order).
What's interesting is that there already was a Sith symbol before this one, but it was primarily (and possibly only) used in Star Wars Legends. While the Lucasfilm Story Group has been slowly but surely reintroducing various story and character elements from Legends back into canon, they've also been making sweeping changes (some at the behest of George Lucas himself). One of them was the Sith's homeworld - which changed from Korriban to Moraband - and now the next step, ahead of Star Wars: The Rise of Skywalker's release, is the official symbol of the Sith Order.