Twitter has applied for registration the word “subtweet” as a trademark which means to write a post that refers to a specific user, but no direct mention of it, as a rule, mocking and critical nature.
If Twitter strikes it rich they will own the word "subtweet" in order to use it for business goals.
Twitter has tried to register the word "tweet" as a trademark but lost because that term had already been in use with application developers.
The word "subtweet" was published by the US Patent Office to sustain objection if there are any. If no one objects to it, Twitter will likely to get the right to register in a few months.