Something that heralds a future event or situation is a sign that it is going to happen or appear.
e.g. ...the sultry evening that heralded the end of the baking hot summer...
e.g. Their discovery could herald a cure for some forms of impotence.
Something that is a herald of a future event or situation is a sign that it is going to happen or appear.
e.g. I welcome the report as a herald of more freedom, not less...
e.g. For her, it was the herald of summer.
If an important event or action is heralded by people, announcements are made about it so that it is publicly known and expected.
e.g. Janet Jackson's new album has been heralded by a massive media campaign...
e.g. Tonight's clash between Real Madrid and Arsenal is being heralded as the match of the season.
In former times, a herald was a person who delivered and announced important messages.