Torn and restored... as simple and direct as that!
A card is freely selected from your deck. You invite a spectator to sign the card.
You take the card between your thumb and index finger and tear off a corner in front of your spectator.
No optical illusion or the like: the corner of the card is genuinely torn, as your spectator can clearly see.
Everything is completely clean! So far, so good...
Now you take the torn corner and throw it towards the card.
At that very moment, it seems to reattach itself in full view and the card is now perfectly intact.
Not the slightest trace of a tear remains! You let your spectator keep it as a souvenir!