1. Download the SIMposium email graphic to you computer. If using this html page "Control click" to "view image" and Command-S to save to your computer
2. Open up Mac Mail
3. Under preferences in Signatures create a new signature and format any textual information such as name, title etc.
4. Drag the SIM signature graphic onto the newly created signature.
5. Copy the image and text, (Press Command-A and Command-C)
6. Start a new message (Press Command-N to create a new message) and Click in the message body and paste in the signature with graphic, (Press Command-A again and Command-V.)
7. Click and Highlight the graphic you want to link.
8. Select Edit | Link | Add... from the menu.
9. Enter the desired address - http://www.simposium2011.com/ Click OK
   
10. Press Command-A once more to highlight all text and copy (Press Command-C)
    
11. Go back to the Signatures preferences window
    
12. Make sure the entire signature text is still highlighted, if it is not, click in the signature and press, yes, Command-A
    Press Command-V, close the signature and preferences tab and quit mail, deleting the draft.
    
13. Relaunch mail and the signature will now be available to use.
    
14. Run a test email with your newly created signature to be sure the link was embedded and now you will have a mail signature with hyper link.

* Note that such rich-text links will not be present in the plain-text equivalent Mac OS X Mail automatically generates for recipients who prefer to read their mail in just text. Also be sure your Mac mail preferences /composing are set to format as "Rich Text."

Additional References

http://email.about.com/od/macosxmailtips/qt/et_sig_link.htm

http://www.alistapart.com/articles/cssemail