I think this is what you do:
Copy the address to your spreadsheet (it's in Google docs, right?)
Go to User Control Panel
Go to Profile
Go to Edit Signature
Click on the URL button that's on top of the big box, and paste the address to your google docs spreadsheet
Press Submit.
I have to get ready for work, so can't help you more, but I'm sure someone else will come along if you need more help.
Have a good day!