To me the advantage of the zip ties is that you don't necessarily have to catch the chicken to read a number. It doesn't help when they are on the nest laying though, the ties are hidden. Let's see, you have 12 chickens. I'll assume the chickens are all the same color.
#1 - yellow
#2 - green...
I don't use numbers. If you need to do that I'd go with another way, wing bands or numbered leg bands.
I make a code from the colors. I don't know what information you are after or how many chickens you have so I don't know what code might work for you. My code is the color of the band on...