The most common and most likely answer to this crossword clue is the 9 letter word REDDENING
I've seen this crossword clue in Independent
R
E
D
D
E
N
I
N
G
Buddy explains!
The straight part
We know that "Showing signs of anger" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case showing signs of anger = reddening.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 REDDENING mean?
REDDENING verb- To become red or redder.
- To make red or redder.
- The action or effect of the verb to redden.