Recently we've been in a battle with some of the webs busier sites regarding our registered trademark.
See, many sites let the username represent the owner of the account like twitter.com/edoceo. Many sites (Tumblr, Wordpress/Gravatar, Twitter and others) make no efforts what-so-ever to ensure that these usernames are not crossing trademarks.
According to their policies you could register "Microsoft" and these sites would not mind (but we know that's not true). However, when it comes to small businesses like mine these sites don't care at all. They are full of lame excuses. It super easy check trademark with an API query (http://edoceo.io/trademark)
On some sites we've identified orphaned accounts, that clearly have no usage and formally requested access.
We're told things like: it cannot be changed, or there are "data integrity" issues. Bullshit.
We know for a fact that at least one of these offending sites is backed by MySQL -
UPDATE is a pretty easy statement.
Other bigger carriers such as YouTube and Instagram do respect the trademark. Simply send them a nice letter, using the provided forms and wait a few days. Done and done.
For now, we're looking for legal council in SF to help us out.
Also, we've made a tool called Username Shop which helps to research as well as buy & sell these usernames aftermarket. At least, until these sites start respecting trademarks.