The Sign Herald Handbook is presently being edited!
In the meantime, here is a handful of customs that are starting to be practiced in the East Kingdom:
Clothing to Wear while Signing:
Solid-colored/not-super-detailed patterns are preferred for wear so as not to distract from what is being signed. Black is not a requirement. Loose sleeves are discouraged. There was traditionally a tabard that the Sign Heralds would wear while signing. The East Kingdom does not have any of these.
Signing Practices at Court (and classes and similar events):
Like new hearing SCAdians, new d/Deaf SCAdians (and single-day visitors) are attending events and picking up on much new vocabulary from the SCA. When an SCA sign is first made in court (Knight, Chivalry, Laurel, Maunche, etc), it is customary to fingerspell the word, sign the SCA word (if there is one) and sign what the award is for. After the first time a term is signed during court, the SCA sign name can be used again throughout the court session. If the event you are signing for has a morning and evening court, as a Sign Herald you are expected to do this step the first time an SCA term is used during each court session, morning and evening.