Take out a silver dollar with the year of your birth on it. Ask a spectator their birthdate. Change the date.

If they're old enough, the whole coin would change.

Now that would be magic.

Maybe not so preposterous using a NW and the duel reality principle.

If you know the birth year ahead of time, it only requires a simple coin switch.

Have a look in T. Nelson Down s's Modern Coin Manipulation.

Somebody already thought about this.

It might work rather well, doing a information peek and having a "coin index" that's similar to a card index in how it works.

Find a spec who is the same age as you and it's a piece of cake...