Hi.
Go to you signature-editing page and type in
"My Blog" or whatever you want it to say. Then highlight the text and click on the button in the tool-bar that looks like a picture of the earth with two chain-links in front of it. A window will pop up that says "Please enter the URL of your link. Insert your blog site, hit "Okay" and you're good to go!
Hope this helps.
Olivia