Everyone has been on a forum or two when it comes to online marketing, and we all know what a forum signature is. Some forums have you post a set amount of times before you can access your signature and add anything to. These requirements are different for each forum, some forums require you to post 25 times while others want you to post 100+. Forum signatures are a great way to get some free advertising out there for your website since it's shown on each post you make on the forum. If you have 100 posts on a forum your link will be on 100 pages, but if you have 1,000 posts your link will be on that many pages. The more posts that you have on a forum, the more chances your banner or link will be seen on that forum. If you can't afford to spend the amount of time it takes to post on these forums to get your banner or link seen, you can always rent someones signature for a small monthly fee
Since all posts requirements are different on each forum, you'll have to post until you can gain access. Usually there will be information on how much you'll have to post before you can gain access to your signature. If you can't find something about the topic, you can always create one which will increase your post count Writing responses to a forum thread will increase your post count as well as writing your own forum thread. Usually posting in a lounge or something similar will not increase your post count because it's just random banter that does not add quality to the forum. Some forums will increase your post count if you do post in the lounge so I do suggest you test it out since you can just ramble on and hit the post requirement in one day lol.
Why Have Requirements?
The forum posting requirements are in place to make it that spammers don't join and just get a free backlink from their pages. If all forums allowed you to come in and post a link, then they would all be covered in spam from the first to last post. The requirements are a good thing when it comes to forum moderation because spammers have to manually post and try to get their links seen while on some forums you can have software make you 1,000 profiles and make 1,000 comments overnight, which is a horrible way to build your online presence and run an SEO campaign lol.
How To Rent A Signature?
A lot of members of popular forums will sell their signature space to make a little bit of money each month. They do this if they don't currently have something they need to advertise of their own. Some members will have a line of text in their signature saying that it's for rent and it could even say a price, but not usually. You'll have to contact them directly on the forum or via skype if they provided their username. Usually a signature link isn't very expensive because the click through rate isn't too high, but that doesn't mean that every forum is created equal. You could find some gold mine signatures on small niche forums that have a lot of members.
How To Sell A Signature (what you're really here for lol)
Selling a signature spot is pretty simple, you can just add a line of text to your sig saying that space is for sale (like how I mentioned above) and people will contact you slowly. You can also go on freelancing websites like SEOclerks.com and post a service saying you're selling signature space for $XX.XX per month and have it set up as a recurring payment. The more posts you have on a popular forum, the more you can charge per signature link since the website/link will be seen more often by more people.
In conclusion, there are a lot of people that sell their signature links and you can be one of them if you put in the time. You can rent signature links if you want some exposure but I wouldn't expect much, at least from my experience since I never got a huge CTR from them.