Window numbering system?
Doesn't matter what system you use if you mark the sashes and the frames the same way and your system provides unique numbers/letters/nicknames/Braille encodings for each window.
1,2,3,4,5...
a,b,c,d,e...
000,001,010,011,100...
John, Paul, George, Ringo...
Eenie, Meenie, Miney, Moe....
I,II,III,IV,V...