The Russian Orthodox cross differs from the Western cross.The cross usually has three crossbeams, two horizontal and the third one is a bit slanted.
The top bar symbolizes the sign that was hung above the head of Christ, it was written: "Jesus of Nazareth, King of the Jews"
The middle bar was where Christ's hands were nailed.
The lower bar is the foot-rest. According to the Russian Orthodox tradition the feet are depicted as being nailed not at one point but individually at the two sides of the footrest.
The slanted line reminds us of the two thieves on both sides of the cross. One of them to the right of Christ ascended to Heaven, while the other one sank to Hell. Thus bottom bar of the cross is like the scale of justice and its points show the way to the Hell and Heaven.
Another interesting fact is that the upper point of the slanted beam always show the way to the North. Thus a church cross can serve as a compass.
During your Moscow tours you'll see churches with other types of Orthodox crosses and your Moscow guide will talk about its symbolism.