calling card

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An engraved card bearing one's full name.
• noun A distinguishing characteristic or behavior.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A small printed card which identifies the bearer, traditionally presented for introduction when making a social visit to a home or when attending a formal social event or business meeting.
• noun idiomatic An attribute, object, or behavior which is distinctly characteristic of someone or something.
• noun euphemistic Excrement, especially of a domestic animal.
• noun A prepaid card or credit card, usually electronically readable, used to pay the charges when making a telephone call.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a card that is used instead of cash to make telephone calls
• noun a printed or written greeting that is left to indicate that you have visited
• noun a distinguishing characteristic or behavior