noun, noun or participle which takes 'suru', intransitive verb
advance warning; prior notice; prior announcement
Used for notice or warning given before something happens. Often appears in negative expressions such as 何の前触れもなく or 前触れもせずに, meaning that there was no advance warning.
予定の変更は、何の前触れもなく発表された。
The schedule change was announced without any advance notice.
彼
He came to the office without giving any prior notice.
noun
harbinger; sign; omen; portent
Refers to a sign that suggests something is about to happen, often a natural phenomenon, illness, disaster, or other coming change. This is a noun use rather than an intentional announcement.
黒い雲は嵐の前触れだった。
The dark clouds were a sign of a storm.
小さな揺れは大地震の前触れかもしれない。
The small tremor may be a warning sign of a major earthquake.