The link is in 3141castro's profile, as I found after writing my post
If I remember right the PPrune rules forbid the posting of links to commercial sites in sig blocks - I seem to remember being pulled up on that when I was promoting a jobs site a site
I agree on the Google ads. Just be very specific on the key words and read the help screens to learn how to control where your ads appear. For example if you are promoting a service in Birmingham UK, use the controls to filter out enquiries that are likley to relate to Birmingham Alabama - no point in paying for irrelevant traffic. (e.g. reject Alabama, USA and the state code AL)