Create back links to your site for better ranking in Google
To improve you ranking in Google you can use backlinks. Allso known as incoming links, inbound links, inlinks, and inward links. Google look at the link from site A to site B as a vote. So if your site has many votes, you will get better ranking in Google.
See Wikipedia's definition of backlinks.
How can you create backlinks to your site?
The essence is to think backlinks to your site when ever you post something on Internet. So basically you should create links to the relevent landing page when posting on twitter, facebook, blog, comments on other blogs, forum posts, your email signature etc.
At SQUIDOO.com you can read an article by Jacki Lee on "How to create backlinks"
What is a sig file and how can I use it for marketing online?
It is really your signature file and you have to stop thinking about is as only contact information. The sig file is a powerful marketing tool. It's been called the secret of email marketing. You can use it in your email, your forum post etc. The sig file must not contain more than six lines and only 65 characters for each line.
Your sig file should contain:
Your value proposition - a good tag line will sum up the benefits and answear "Why should I care?"
A direct link to your offer - use a link to the landing page rather tha the url to your home page.
Multiple ways to contact you - telephone, fax, email, and possibly snail mail. Remember: You only have six lines so you may have to priorities.
On Clickz.com you can read an article of Debbie Wall - "Making the sig file market for you"