The most common and most likely answer to this crossword clue is the 4 letter word AGMA
A
G
M
A
Buddy explains!

The straight part
We know that "Symbol" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case symbol = agma.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 AGMA mean?
AGMA noun- The nasalized velar consonant found in such words as song or wink.
- The symbol ŋ, used to represent that nasal velar consonant in IPA; eng.