Leg bands are the easiest to see. they do come in different sizes, so if your concerns are about using zip ties, here is an option. These will not kill your chickens legs.
https://www.amazon.com/001-100-Reus...773675&sr=8-2&keywords=chicken+leg+bands+16mm
https://www.amazon.com/001-100-Reus...773675&sr=8-2&keywords=chicken+leg+bands+16mm