I'm not sure that's possible even if you tried... Keep an eye on newly registered user's - if their usernames are suspicious then ban them.
Also, filter domain related words such as .com, .net and .us and hotel names to prevent anyone stealing your users.
Remember to filter every possible way of advertising (E.G. Using "Habbo"):
Habbo
H a b b o
Hábbó
H4bbo
H4bb0
etc.