I use colored zip ties when they get older but nothing when they are really young. That's not important to me but it is to some people. My issue with using zip ties when they are really young is that they grow really fast. You have to keep up with checking them and replacing the zip tie before it gets too tight. You can do it but you need to work at it. Same thing is true if yo get the rings.
I don't know how many chicks you are talking about or what colors, but you can die the down to identify individuals. Use a different colored permanent marker or even the same color and mark the down in different areas. Many hatcheries will use food coloring to mark the foreheads of chicks of different breeds but the same down color if you ask them to. Obviously don't use black on a black chick or yellow on a yellow chick, but you can work up a code based on where you mark or what color you use. A mark on the head, chest, right wing, left wing, small of the back, right rear side, etc. Marks on the chest plus right wing would be a different bird than chest and left wing. You get the idea. Different colors give you other options.
This also requires maintenance. Chicks pretty rapidly shed and grow new feathers or the marks might wear off. You have to keep up with it but it might work better than zip ties or rings on those tiny feet and legs.
I've hear of people using fingernail polish on the claws, different colors or on different claws, but I'm no sure how fast those wear off. I think anything will require maintenance when they are young and growing.
