This design is also called a staurogram or monogrammatic cross.  It dates back to an early manuscript from the second century when the Greek letters T & P were superimposed over each other and used in the early Greek New Testament (175-225 AD) as a symbol of Christ's crucifixion.  It was later used on a coin struck in Constantinople between 507-518. The crown is a later addition.  A historical religious symbol, it was replicated and placed on the sterling silver shield pendant with the raised cross and smooth border.  Makes a great religious gift for that someone special or as a symbol of faith.  

Thin border; Attached sterling silver bail; Smooth, mirrored background; Raised central image.

Height: 1 1/2 inches with bail

Width:  15/16 inch

Weight:  6.6 grams

Chain included.