Well, it would still be a training flight, just one that hasn't reached it's aim. So it would still be P/UT for them and P1 for me.
You could annotate the flight as "unsatisfactory" if you wanted to be a complete ar*e, but I simply wouldn't sign the logbook or put my licence number against it.
You can't be forced into signing anything you don't wish to. Especially as you are supposed to be signing to say that something has been achieved, when it hasn't.
And no signature or licence number means no revalidation, unless the signature gets forged.
Enjoy your flight.