[syn: calling card, visiting card, card]
3.  a distinguishing characteristic or behavior; 
- Example: "bombs are a terrorist's calling cards"
WordNet (r) 3.0 (2006):
calling card
    n 1: a card that is used instead of cash to make telephone calls
         [syn: calling card, phone card]
    2: a printed or written greeting that is left to indicate that
       you have visited [syn: calling card, visiting card,
       card]
    3: a distinguishing characteristic or behavior; "bombs are a
       terrorist's calling cards"
Moby Thesaurus II by Grady Ward, 1.0:
19 Moby Thesaurus words for "calling card":
   ID card, badge, calligram, card, countermark, countersign,
   credentials, dog tag, identification, identification badge,
   identification tag, initials, letter of introduction, monogram,
   press card, serial number, signature, tessera, visiting card