So you want to get a TM on Volsh and try and force anyone that is using that for their user name to change their name or hand over their account to you?..
Trademarks are limited to a certain trade.
You cannot make an apple computer..
You can have an Apple Shoes, or an Apple Jeans, or an Apple Hardware Store.
Is he really using your name in the same trade? If not, good luck. If he was first, good luck...
If I wanted to call myself "Coke" as a forum user name, I could..
If I wanted to sell beverages under that same moniker... uhhh... no..
If the user is doing trade under that name in the same business you are in (and/or leading people to believe they are you) on the same forum, then yes you potentially could build a credible case against the person / company behind that user name.
Though, it often may be easier and less expensive to present your case, in a matter of speaking, to the forum operator and strongly request they reassign / block that user name due to TM issues / passing off. Most forum operators will do what they reasonably can to avoid potential legal problems, including reassigning (especially inactive for long time) / blocking names, deleting posts, removing links, etc.
Keep in mind though this goes both ways - they could fight back and demand that same username on other forums where it's already been assigned to you. Could get nasty, especially if they have a strong TM claim and/or are well known under that username by others - they may gang up to retalate with negative posts, DDOS against your website, etc.
With all that said, if the username has been long inactive on the other forums - contact the webmaster and see if they're willing to reassign it to you or at minimum suspend the name. If the username is active, try contacting the user - perhaps they'll be willing to change it / stop using it in exchange for something, such as free stuff, money, etc.
And they already have the same user names and have for a period of time.