Patriarchal cross

The Patriarchal cross is a variant of the Christian cross, the universal religious symbol of Christendom. Similar to the familiar Latin cross, the Patriarchal cross possesses a smaller crossbar placed above the main one, so that both crossbars are near the top. Sometimes the patriarchal cross has a short, slanted crosspiece near its foot. This slanted, lower crosspiece often appears in Byzantine Greek and Eastern European iconography, as well as Eastern Orthodox churches.

The symbol, often referred to as the patriarchal cross, appeared in the Byzantine Empire in large numbers in the 9th century. In the Byzantine Empire of the 9th century, the double cross was not a religious, but a political symbol used by Byzantine clerks and missionaries.

Source: http://en.wikipedia.org/wiki/Patriarchal_cross