“As it turns out, even Meta-formerly-Facebook has a federal trademark, which it registered in 2019, for a blue-and-white letter "X" — and it's directly related to "social networking services," presaging even more drama for Musk's troubled microblogging site.”
https://futurism.com/facebook-owns-trademark-x-social-media
https://futurism.com/facebook-owns-trademark-x-social-media