Part way down on this page there is a section called Adding a signature http://help2.talktalk.co.uk/webmail-features I don't use Talk Talk so no idea if this is for the new webmail you mention, I just found this by doing a web search.
Many thanks, VHG I had been in Settings menu, but obviously didn't scroll down far enough. Got sorted, but I wish they'd left things alone, and not convinced new email is working properly yet.