I am using this forum from past few months. Now I am enable to add my own signature. So I want to know how many links I can add in my signature? And what is the time period to change them?
What if I want to use new signature every month? Right now I have four links in my signature. Is it okay?
Experts please reply.
I assume you are asking for “SEO” reasons; the information on signatures is here: http://www.sitepoint.com/forums/faq.php?faq=youraccount#faq_signatures
The part you may be interested in is “Note that SitePoint is a no-follow forum. You will not receive a backlink from your SitePoint Forums signature.”
Not exactly but yes!
Actually I have many websites which I can have in my signature that’s why I asked. I own some small businesses and provide different services using different websites.
But please remember to read the guidelines in the link Rubble provided, especially the bit that says
Your signature’s size is limited to 4 lines of 65 characters each.
There used to be an auto-limiter that prevented members’ signatures exceeding the 65 character limit, but it doesn’t seem to be working at the moment, so I’m afraid you’ll just need to count. 
Yeah, I was using more then 65 characters per line… thanks for your attention. I have edited my signature. Hope it is perfect now.
Actually, no it wasn’t, because you’d included HR tags, which are not allowed. (I have removed them.)
Please check all the signature guidelines:
Create your personal signature in line with these requirements:
Your signature's size is limited to 4 lines of 65 characters each. BBcode isn't included in the total number of characters in a signature.
You can include links that lead to your site(s) or a product page.
You can include a slogan (for instance, "UK's Best Hosting starting at £19.99").
You can't include affiliate or referral IDs. (Links to Outwar and similar types of schemes are acceptable, as these are links to games.
It should be obvious from the outset where any link leads to.)
You can't use short URL services (such as TinyURL) in signatures to get around the points above
You can't promote scams or make unenforceable offers (for example, "Earn $10,000 a month selling suntan lotion to dolphins").
Pre-approved BBcode can be used, but must adhere to the following restrictions:
Center and right-align tags can't be used.
Code, Quote, PHP, HTML, Edit, Off Topic, Spoiler, Highlight, and HR tags can't be used.
The largest font size permitted is size 3.
Your signature can't contain images, but it can include smilies.
Signatures can't be bought or sold, nor can they contain offers to buy or sell other signatures. This guideline includes linking to web sites that solicit the selling of signatures.
Any attempt to include a 'hidden' signature will be removed and the user may receive an infraction.
Note that SitePoint is a no-follow forum. You will not receive a backlink from your SitePoint Forums signature.
As long as you follow the rules that TechnoBear has posted a copy of, you can arrange your signature however you want. You can have as many links as you can fit into 65×4, and you can change it as often as you want. (Note that your signature displayed is always your current one, not the one you had at the time you made the post)
You might also want to bear in mind these guidelines, from elsewhere in the FAQs:
All posts in the forums are easily found via search engines, so unless you’re willing to expose your information to the world, please do not post telephone numbers, e-mail addresses or IM nicks in your posts. For your own security, keep private information like that - private.
Posting your e-mail address could result in you receiving a lot of spam.