Um, you do know the hand stamp would have washed off in your shower that night, yes?
I like to imagine that the Mark of the Beast is somewhat more permanent and subtle.
And You Do Know that Satan is the great deceiver, right?
Just because the offer is made in the form of a jest, doesn't affect your acceptance of it one bit.
It just means Satan "tricked" you.. ( Doh! )
It is the acceptance, not the medium that is permanent.
The physical mark may wash off the body, or be removed by other means, but the mark upon your soul is permanent.
It cannot be hidden from Satan, or from God.