As paddywak (love that handle) chickens are usually IDed with different coloured leg rings [bands]. These rings are basically a piece of 5" pre-stressed plastic that, when let go curls like a slinky, around the leg. Very hard to loose and easy to put on.
These are also split aluminium rings and even permanent whole ones that have to be put on when the chooks are chickens and the legs grow into them. The permanent ones are impossible to remove with breraking the leg and often used with more valuable rare breeds.
Chickens do have ears but they are hidden under feathers and do not have the lobes needed for attaching jewelry :�)
In some asian cultures they decorate their chickens on festive occasions.