Counterfeit Hollingworth - Different Cards?

[CrazyClement]

Starting on this brilliant effect (great concept) but I have three questions:

1) Has anyone tried using different cards but same back?
2) Has anyone tried signing it an s**t*h it? (Don't want to expose it, hope you get what I mean)
3) Can I not use the lighter? In places with smoke detectors.

Thanks!