Is there any benefit to sign up for a forum which doesn’t pertain to your niche just because it has a do-follow signatures?
This question also pertains to blog commenting? Does it matter if you comment on a non-niche blog?
Well, it probably won’t do harm, but it’s probably pointless as well. Google prefers links to be from sites of related content, but I’m sure it’s smart enough to know the difference between blog comments and real content. Be sure not to go posting fluff on websites just for a backlink. This is both useless and uncivilized.
Right click on this page. Click “View Source”. Now count the number of <a> tags. Several hundred, typical of a forum.
The PageRank any given link on a page gains from that page is the page’s PageRank divided by the number of links. The average forum thread has a PR of 0; it’s very far from the domain’s root where most of the PR is concentrated, and has only one or two backlinks, also from deep pages elsewhere on the forum.
0.01 PR / 300 = ~0. In other words, links from forums are worthless, even if they’re “do-follow”. You’re wasting your time even thinking about them.
After reading this, i am planning to make catchy and meaning ful signature link to increase visit. And i should use forums to increase visitors not for page rank.
But from some other articles, i came to know that Do Follow link from signature help to increase ranking on particular keyword, so may i be continue with forum posting to increase ranking of my website?
It certainly can help, but forum links from non related forums bring just about half of the link juice from the related ones.
Did you really read it? 
You raise a good point Dan. I always knew that forum sigs don’t hold that much value, but makes more sense now.
Yes it is worthless to get links from unrelated forum. you will just get a dead link for you website that have no use in ranking. It just to increase your baclinks quantity.