INRI stems from the Latin phrase"Iesus Nazarenus Rex Iudaeorum'' meaning "Jesus of Nazareth, King of the Jews". This was the notice Pontius Pilate nailed over Jesus as he lay dying on the cross. It now signifies that a true Christian lies there.
The Budded Cross with three circles or discs at the end of each arm, in a Christian context, represents the Holy Trinity: God the Father, Son and Holy Spirit.
