Ask HN: Getting your company username on social media

Search for "<Facebook|Twitter|GitHub|etc.> trademark policy" on Google ;)

When it comes to legal stuff, it's a lot more easier to find someone to talk to. And most of these sites are providing usernames on a first-come, first-served basis. If someone has it but not actively using it, you can also report this inactivity and ask them to make it available to claim.