Artist's rendition of the saltire/Derafsh Kaviani labarum pattern per A. Roes
A. Roes, An Iranian Standard used as a Christian Symbol , The Journal of Hellenic Studies Vol. 57, Part 2 (1937), pp. 248:

"... vexillum on which the diagonals are indicated; in the four sections thus formed four balls are sometimes added.(...) Tassels occasionally fringe the lower edge of the cloth. It occurs on the coins of many Roman emperors of the IVth  and the Vth  centuries; on going through the imperial coins in the British Museum I found it on those of Constantius II, Valentinianus, Jovianus, Gratianus, Valens, Arcadius, Constantine III, Jovinus, Theodosius I, Eugenius, and Theodosius II"
"The emblem was not confined to the standard alone: the rectangle with its diagonals and the four dots occasionally has a prominent place in the decoration of the robes of the emperors;(...) this shows that the rectangular frame was not merely the border of the vexillum, as one might be inclined to think, but that it formed part of the symbol itself."
This vector image includes elements that have been taken or adapted from this file:
Original file by TRAJAN 117 Modified by  Odinatra