If you were transported 400 years into the past with no clothes or anything else, how would you prove that you were from the future?

@Henny [quote]I am clean shaved below and I am prety sure they did not do so back then[/quote]

There's a difference between not doing it then, and whether or not it's possible to do it. 400 years ago, it would have been possible for someone to shave down there.