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The papal cross is a cross that has become a symbol of the pope and is carried in front of him during all papal processions. The top two bars are to represent the two criminals that died beside Jesus Christ and the third bar represents Jesus.
This cross is not displayed in protestant churches, because of the attachment that the cross now has to the pope.
One similar cross is the Russian Cross, also known as the Eastern Cross. It is common in the eastern orthodox groups.
Sources:
Byzantine
http://www.bright.net/~gray0013/symbols/cross.html | 
