Labarum of Constantine I (Vexilloid of the Roman Empire). Drawn after File:As-Constantine-XR RIC vII 019.jpg; the three dots represent three "medallions" or portraits that could not be rendered in detail on the coin, c.f. File:Konstantin den stores labarum, Nordisk familjebok.png 
c.f A. Macgeorge, Flags, Glasgow, 1881:

"The vexillum was a standard composed of a square piece of cloth fastened to a cross bar at the top of a spear, sometimes with a fringe all round, and sometimes fringed only below, or without a fringe, but draped at the sides, When placed over the general's tent it was a sign for marching, or for battle. The labarum of the emperors was similar in form, and frequently bore upon it a representation of the emperor, sometimes by himself and sometimes accompanied by the heads of members of his family. [...]"
Labarum_of_Constantine_I.svg (reconstruction by Eugene Ipavec, 2006)
Vexilloid_of_the_Roman_Empire.svg
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