We found this interesting information by Stacy Calvert on eHow.com., which we’ve excerpted:
Simple and personalized, they carried meaning not conveyed by text, but rather in the way they were physically manipulated before being left at the home of a friend, acquaintance or potential social connection.
If a card was left intact, it meant it had been delivered by a servant; if bent or torn on the top right corner, it signified congratulations. On the top left, a social call. On the bottom left, goodbye. A calling card bent at the bottom right acted as a Victorian-era sympathy card.
A black border on the card meant the caller was in mourning. Popular symbols, such as birds, flowers and hands indicated sentiments, such as friendship and peaceful intentions.