'calling card' definitions:

Definition of 'calling card'

From: WordNet
noun
A card that is used instead of cash to make telephone calls [syn: calling card, phone card]
noun
A printed or written greeting that is left to indicate that you have visited [syn: calling card, visiting card, card]
noun
A distinguishing characteristic or behavior; "bombs are a terrorist's calling cards"

Synonyms of 'calling card'

From: Moby Thesaurus