Give them a one-of-a-kind business card.
I am actually opposed to the idea of using term 'business card' as such term only refers to the notion of promoting a business the card owner has. I initially want to come up with using term 'name card' as it seems to give more freedom on the content of the card (as long as it has name of the giver). However, dictionaries such as Webster, Oxford and Thesaurus do not acknowledge 'name card' as most of us do.