In Outlook 2007 -

Go to Tools
Options
Mail format
Signature

Create a new signature or use an existing one

Copy or know the appropriate URL or email address

Once signature block is typed in, highlight text with cursor and find icon that looks like globe with a link on it. (mine is at the right of the tool bar)

Select link icon and a menu will open with options for e-mail or links. Select option you want from the left column and paste or type in information. Can also include the text to display vs the URL.

OK

If you have more than 1 signature, indicate when each is used.

Ok