chrismon

noun3

1. •
   A Christogram.

   • The sacred monogram or chrismon was extensively used by Constantine […] a crown of gold, enclosing the chrismon or mysterious monogram — 1869
2. •
   A stylised siglum or character interpreted as an invocation of Christ in Merovingian and Carolingian documents.

   • The document usually begins with a verbal invocation (such as In Dei nomine, amen) or a chrismon (often Christ's monogram formed from the letters XP) — 1970
3. •
   A Christmas decoration with explicitly Christian religious symbolism.

   • Chrismons were first made as tree decorations by members of the Lutheran Church of the Ascension, Daville, Va., in 1957. — 1964