"If you're tempted to mark your chicks in some way, it's important that you don't artificially create “differences” that will draw attention and become a focus of obsession. Especially refrain from using anything red to identify any of the chicks. Keep chicks as uniform in appearance as possible."
@azygous I had planned on using small pieces of blue drinking straws, numbered, just to help keep track of my babies. Thoughts?
https://www.backyardchickens.com/a/aggressive-baby-chicks-and-how-to-stop-the-behavior
It's wise not to use anything that might end up in a chick's crop. They are babies, and just like human babies, things like bands on their tiny legs are risky as choking hazards if they come off. And don't underestimate the ability of chicks to get things off their their legs and into their mouths.
If you need to mark them, use a colored permanent felt marker or nail polish.
I've tried using plastic hair bands to mark chicks, and it was tempting because they're cheap and come in all sizes and colors. But even the smallest size will come off, and if they don't fall off, the chicks grow so fast that I failed to notice until a band was constricting the circulation of a chick's leg.
You have the benefit of my stupid mistakes, so your chicks don't have to suffer any mishaps. Luckily, I caught the problem in time, and no real damage was done, but it was a close call.