In Gmail, any websites addresses in signature are automatically converted in to hyperlinks. For example, if you have added signature with web address and when you do a compose new message, it will automatically display the web address as hyperlink.

There is no settings that is currently available in Gmail that would turn off these hyperlinks. But there is a work around which can be done for each individual email message.

Clicking the Compose Mail button would open a new compose mail window populated with signature. Now click the Pain Text option above the message text area to remove the hyperlink. In case if you plan to use other formatting option for writing the email then click the Rich formatting option. By this way you can manually remove the hyperlink from the web address in Gmail.