Both Uses of

herald
in
Oedipus the King

JOCASTA They were but five in all, and one of them A herald; Laius in a mule-car rode.†
*

Then, lady,—thou shalt hear the very truth—As I drew near the triple-branching roads, A herald met me and a man who sat In a car drawn by colts—as in thy tale—The man in front and the old man himself Threatened to thrust me rudely from the path, Then jostled by the charioteer in wrath I struck him, and the old man, seeing this, Watched till I passed and from his car brought down Full on my head the double-pointed goad.†

Definitions:

(1) (herald as in: heralds the coming of...)
a sign that something will happen -- especially something important and good

or:

to announce or welcome -- especially with enthusiasm
(2) (herald as in: announced by herald & trumpet)
a person who announces important news -- especially a king's representative
(3) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely, herald can also refer to an official whose specialty is heraldry (the study of coats of arms -- symbols once used to signify the right to bear arms).

Historically a herald was a person who made announcements at jousting matches, or (much more rarely) any prestigious assistant in a dignified setting such as a courthouse or royal palace.