Org admins have the ability to add a company message that displays to all users. Should you like, you can add a link to this message as well.
Here is an example of a company message with a link:
Your message is: "To learn more about Autodesk click Here." To add a link to the word "Here" you would edit the text as such in the message box:
To learn more about Autodesk click <a href="http://www.autodesk.com">Here</a>.
The <a> is where the link starts and the </a> is where the link ends. The text in the quotations will not be visible.