Tessa Padden is the only Tessa I can find who worked on 'Sign On'. You can contact her via nordaf at http://www.skd.ndirect.co.uk/nordaf/directory/bsl. htm
and perhaps ask her if she knew any other Tessa? Or you could try emailing Channel 4's current programme for young deaf people: [email protected] as there doesn't appear to be a site left for Sign On itself. Hope this helps.
The same question was asked by Heather 4 days ago. I did a lot of research but couldn't find any other Tessa listed as having appeared on the show. No other answers were posted.