Effect 1.
The spectator's signed card turns into the Trump card. Then just as quickly vanishes as it turns out to be "Fake News".
Effect 2.
The spectator signs the Trump card. Then says the magic words "I didn't sign it. Nobody saw me sign it. You can't prove anything". And the signature has disappeared quicker than a list of names in a mysterious file.
The gimmicks provided allow you to come up with your own routines too!