What does the cryptic crossword clue "Indication submariner is surfacing (4)" mean?

The definition is "Indication". The wordplay uses a reversal. NEMO (reversal="submariner") = OMEN; definition: "Indication" The answer is OMEN.

Indication submariner is surfacing (4)

Guardian Cryptic #28935 | 1 Down | 2022-12-08 flower