Under what condition one may use branded stuff ? (for gaming clan needs)
Dirty bomb brand copyright
MissMurder is out-of-office at the moment I think (due to her sister having a baby yesterday) so it’s doubtful she will be able to respond today. :s
I am fairly certain I’ve seen this answered somewhere before though x-x Are you asking about using branded stuff for a gaming clan as in sponsorship? I’m sure the terms of service will detail this somewhere, but if you are able to comment more on the context of the “branded stuff”, I might be able to help ^.^
i want to prepare giveaways for our clan and public for example mousepads and all that small things players use every day with dirty bomb content on it.
I believe you can use DB logo for a non profit - that means you cannot sell stuff with DB branding on it.
But I think it would be the best to wait for missmurders/nexons reply.
edit: seems like thats exactly what you want to do. Well, contacting nexon is your best bet.
Since MM is out of the office you could hit up OneLetter on Twitter. https://twitter.com/OneLetter
OK, so as with any regular IP, copyright states that if you were to use the logo on any personalised merchandise (such as the mouse-pads you suggested, like the ones from http://www.vistaprint.co.uk/mouse-mats.aspx ) you would require permission from the copyright holder - in this case, Nexon or Splash Damage - due to the fact that you aren’t technically allowed to produce custom content like that without consent.
I would say, if you were making one solely for yourself, there is very little they would do to stop you and it’s doubtful they would even find out anyway - but, if you are creating products to be given away like that, that’s a little different.
My best suggestion would be to message @MissMurder directly through http://forums.dirtybomb.nexon.net/messages/add and await a reply. Bare in mind, you may not get a reply until Monday or Tuesday next week at the earliest, but you will get a definitive answer that way.
I would also suggest including some examples of what you wish to produce (such as the mouse-pads you said here), because these specifics will need to be covered when asking for permission - due to legal reasons.
Hope this helps a little bit! 
Yeah, but the copyright stuff (from my experience) usually does the publisher, Nexon in this case.
I could be wrong through.
JohnS is correct. While Splash Damage own the IP, due to Nexon being the publisher, I am fairly certain it will be them who deals with the legal technicalities of the IP.