5 Answers

I,m an Athiest but I would guess, Father ,Son, Holy spirit.

Wow religous depecitons of this kind are tough.  I can tell you what three crosses mean the center cross represents Christ. The othe two represent the theives that hung on both sides of Christ.  Such meaning is important for the Chrisitan belief.  It's a human value your neighbor holds dear.

Adding to the answer you received from Lbarnett:   Christians believe that Jesus was born on or around Christmas (12/25).  His life is documented in the Bible.  He was crucified on a cross along with two other "criminals".  The death of Jesus is seen as a sacrifice for all mankind to atone for their sins.  The point of displaying the three crosses at Christmas is most likely to symbolize the true meaning of Christmas, which is ultimately the sacrifice Jesus eventually made.  
My Christmas card this year is an acrylic painting I made of a diorama (the outer part resembling a wrapped present, the inside showing Calvary in the background with the three crosses, and the nativity scene in the foreground.  It's pretty cool.   

Maybe their Christian?

And this harms you how?????????