Here is a link to a great article about Calling Cards. Also, here is an excerpt:

“During the 1800’s and early 1900’s the practice of “calling” upon or visiting one’s relatives, friends, and acquaintances was a middle and upper class social ritual governed by countless rules and traditions. Central to visiting etiquette was the use of the calling card. Every gentleman kept a ready supply of calling cards with him to distribute upon his visits. When calling upon a friend, a gentleman gave his card to the servant answering the door. The servant would be holding a silver tray and the card would be placed upon it. If the person the gentleman was calling upon was home, the servant would take the card to them and they would come meet the gentleman. If the person being called upon was not home, the servant would leave the card for when they returned.

Generally upon a gentleman’s initial visit to a home, he would simply leave a card and then depart. If the new acquaintance wished to formally visit with him, he or she would send a card in return. If no card was sent, or the return card was sent in an envelope, this signaled that the new acquaintance did not wish for a personal visit to occur. This signal (the card in an envelope) could indeed be sent after any visit in which the visited party no longer wished to be called upon by this particular person. It was basically the well-mannered brush off. A calling card was also used when a gentleman was desirous to see someone at a hotel or parlor. He would send up his card while he waited in the reception area or office for his acquaintance or business associate to come and greet him.

A man’s calling card was simple and plain in design. About the size of a playing card (they were toted about in a carrying case tucked in one’s breast pocket), they bore a man’s name, and later on, his address as well. The name was written in the center, sometimes with a middle initial and sometimes not. A young man did not preface his name with “Mr.” A military officer included his rank and branch of service. A physician could include his professional title, as in “Dr. Robert Smith,” or “Robert Smith M.D.” But honorary titles such as Prof., Hon., and Esq. were not acceptable. The card sometimes also included the name of the gentleman’s club or fraternal organization a man belonged to.” Read more here.