Circlets for all ranks (or: what does that hat stand for?)

Plain bands: okay for anyone

Ornamented or engraved bands: AoA's

Jeweled Bands: Grants

Any band bearing the device of a Peerage: that peerage

a band or circlet ornamented in 'pearls' [pearls or stone pearls] -
Baron/ness, both landed and Court

Circlet with points: Viscount[ess] Prince[ess] of a Principality, any number
of times

Circlet with embattle top edge: Count[ess] -ruler of a Kingdom once

Circlet with Strawberry leaves on top: Duke[ess} ruler of  Kingdom at least
twice

Circlet of golden Laurel with Amyathests in center front: Royal Highness
[soon to be King/Queen]

Really ornate [and heavy] crown: King/Queen

I think this is right for An Tir.  Different kingdoms have different laws.