I've gotten many of those registrations from *****@mail.ru in the past myself, I'm a local forum so someone from Russia would not have any interest. They are most likely bot registrations and unless you have it disabled you'll see they have their link in the website field. Some will eventually start posting. Usually something stupid like "I agree with that" etc.
They want inbound links to their site. Even if they do not have the website field in what they'll do is post a few messages like the one above, hope they don't get caught, then come back and fill in the signature field at a future date when the post has been buried and/or fill in the website field.
The other method is they'll post some legitimate looking links, "Check out these cool pictures" which will go to legitamte cool pictures... :) After a week or two they'll do a redirect to spam page on their server. May even be in combination with editing the post... You're none the wiser because the post has been buried.
I simply denied the use of @mail.ru since there was so many of them. That is really not a very effective because they can use any amount of email addresses. Depending on the forum software you are using there are things you can do to prevent them from signing up in the first place.
I'm only familiar with phpbb but the only sure fire method I've com across is to ask a simple question. For my forum I have a line of text that is above the registration. Within the paragraph is underlined word, the question the registrant has to answer is type in the underlined word above. Simple for anyone to understand and still accessible for the visually impaired.
I've had 0 spam posts or regitrants in about year now, the reson it's so effective is because it's not standard on a phpbb forum. Addtionally the question and answer is particualr to my forum. They don't make bots that smart. ;)