Happy Pi Day 2017! For this day we have two Pi Flags that read a 3.14; one is from the NATO number system the other is from the International Maritime number system.
By queer coincidence NATO and International Maritime flags use a red, crossed flag for the number: four. This fateful convergence of math with vexillology allows both Pi flags to be centered on a quartered pie. For NATO the central element of the number four is sliced at 45 degrees, but for International Maritime the pie is cut at 90 degrees.