The Brazilian π Day Flag

Canadian π Day Flag

Alternatively, it can be used in Peru too!  For the record Peru's flag came first!

Spanish π Flag

Persian π Flag

Pi is considered a sacred number, what better way to have it stylized like modern Persia's flag.  In this case the number Pi is written in Arabic along the white stripes on the edges of the red and green stripes.  Likewise the central portion has the iconic symbol of Pi. 

National Greek π Flag

The national Greek π flag has 3 white stripes to represent three, 1 blue canton to represent 1/10th, and four blue stripes to represent 4/100ths of the number Pi, which equals 3.14.

Greek Numbers Pi Flag

Since the Greeks originally used letters to represent numbers, we have a flag that reads 3.14.  Gamma is the 3rd letter and is capitalized. Alpha is the middle letter which represents one, but it is lower case because it is a fraction.  Finally delta is the 4th number/letter.  

π Flag for the Tridecimal Base - 13ths

There is more than one way to look at π.  The dominant view is this number is 3.14 but that is an artifact of the decimal system.  Taken from another base, say like the number 13, π becomes the number 3.1AC1049052A2C.  Now how many people can recite that sequence from memory?

Like all the π flags out there, this one is based upon the first three digits of π from the tridecimal, base system of 13 digits, which is 3.1A.  The number 3 is the whole number represented with the international maritime flag for three, which looks like a reverse flag of the French.  Then the number one is the red dot on white in the middle, which looks like the Japanese flag.  Finally the Alpha flag with is white and blue swallowtail design.  Since the international maritime flag for the letter A does has a missing sector this give the central portion a Pac-Man like look.