The most common and most likely answer to this crossword clue is the 4 letter word OMEN
O
M
E
N
More clues leading to the result OMEN
- Sign depicting old fellows
- Sign suggesting an absence of people?
- Sign from ladies losing weight
- Forecast given by royal servants you once ignored
- Warning enigmatic sea captain rebuffed
- Writing on the wall round gents
- Old blokes writing on the wall?
- Sign name in Latin when dispatching note
- Potentially bad forecast captain rejected
- Ladies missing whiskey could be a bad sign
Buddy explains!

The straight part
We know that "Warning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warning = omen.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OMEN mean?
OMEN noun- Something which portends or is perceived to portend either a good or evil event or circumstance in the future, or which causes a foreboding; a portent or augury.
- A thing of prophetic significance.
- To be an omen of.
- To divine or predict from omens.