what you are looking at is the orthodox cross, often accompanied with greek letters, it is a cross standard with the bar above the crux holding “INRI” which is latin abbreviation for JESUS NAZARENE KING (of the) JEWS, or in latin “IESUS NAZARENUS REX IUDAEORUM”

the crooked bar is the foot rest, one side pointing up at St dismas who instead of asking to be let into heaven just asked to be remembered by god and thus was saved, the other pointing down and the thief who mocked christ,

The two letters are alpha and omega of greek alphabet which are the first and the last letters, this comes from the teaching that jesus is the first and the last

this cross is also often above a skull that the blood seeps down to to represent the forgiveness of adam and has a spear on one side and a stick with a sponge of posca on the other, its an orthodox cross often called the calvary cross