Zip ties work well but be very careful with them! You need to put them tight enough so the chick does not get it off. The problem: chicks grow so fast they quickly get too tight and will cut off circulation. I have a friend that had to cull a chick because she did not take it off in time. She is still traumatized.
The bands you buy will expand when the chicks grows. You will need to buy larger sizes as the chickens grow but since the expand you don't have to watch em quite as often.
I often use paint. I use non-toxic paint and put a dot just above their combs and partly on the comb. The paint usually lasts 2-3 weeks. You can re-paint or put a leg band on them at that point.
Good Luck,
Deann