There has been a good webpage about these recently (with pictures), but a Google search is failing to find it at the mo.
I seem to remember reading that although they were flown by RAF crew and carried British national markings that they still retained their American serials.

Edit, some good info and pictures on the missions (op Ju Jitsu) here, http://www.spyflight.co.uk/scul.htm, it looks like the Tornados’ didn’t carry their serials during the actual missions.