The most common and most likely answer to this crossword clue is the 4 letter word YONI
Y
O
N
I
Buddy explains!
The straight part
We know that "Sex symbol" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sex symbol = yoni.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 YONI mean?
YONI noun- The vulva or vagina, or a symbol of them, especially as an object of veneration within certain types of Hinduism, Buddhism, and other cultures.