Can a fake parking ticket save you from a real one? That is, if a parking inspector sees a ticket - any ticket - on your car, would they just ignore you? I doubt anyone would tell you. To find out, you'd have to park illegally and put a fake ticket on your own windscreen, then watch a parking inspector walk by your car.
The difficulty with this type of decoy would be that the inspector needs to be fresh on his shift when he encounters your car (so he can assume the ticket was placed by someone else legitimately) or needs to forget that he didn't do it himself. It's probably not a foolproof plan, then, but might work just well enough for some habitual bad parkers to be worth it.
Mokalus of Borg
PS - My best guess is that you can still get more tickets if you've already got one.
PPS - So, in that sense, it's absolutely no help at all.