Ornate Crest Details?

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Is there any historical evidence of any artistic details of Crests?

I guess what I am asking is... The curved part usually wood? Where there any that had carvings or engravings in them? Anything that was added to it? Brass, Bronze?

I am asking not only about Centurions, but Legionaries as well.

Were they plain? Would any of them have a design on them that would distinguish their Legion or Cohort?

Would a soldier have been allowed to customize it? Just curious... when designing my Kit and Impression. Thinking ahead. Thanks for any input.

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I guess I am also asking because I have heard that Legionaries and Centurions were able to customize their belts... would this be applicable to any other part of their armor or clothing?