The most common and most likely answer to this crossword clue is the 4 letter word RATS
I've seen this crossword clue in The Guardian
R
A
T
S
More clues leading to the result RATS
- Heartlessly declaims traitors
- S-sailor upset to see these leaving ship
- Bother celebrity in retreat
- Oh no: celebrity’s on the rise
- Blast it! Lead’s overturned
- Vermin running around two state capitals
- Damn sunrises!
- Sun rising? Nonsense!
- Sings lead after comeback
- Expression of annoyance from celebrity performing U-turn
Buddy explains!

The straight part
We know that "Sings" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sings = rats.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 RATS mean?
RATS noun- A medium-sized rodent belonging to the genus Rattus.
- Any of the numerous members of several rodent families (e.g. voles and mice) that resemble true rats in appearance, usually having a pointy snout, a long, bare tail, and body length greater than about 12 cm, or 5 inches.
- A person who is known for betrayal; a scoundrel; a quisling.
- An informant or snitch.
- A scab: a worker who acts against trade union policies.
- A person who routinely spends time at a particular location.
- A wad of shed hair used as part of a hairstyle.
- A roll of material used to puff out the hair, which is turned over it.
- Vagina.
- Short for muskrat.
- (usually with “on” or “out”) To betray a person or party, especially by telling their secret to an authority or an enemy; to turn someone in.
- To work as a scab, going against trade union policies.
- (of a dog, etc.) To kill rats.
- A scratch or a score.
- A place in the sea with rapid currents and crags where a ship is likely to be torn apart in stormy weather.
- To scratch or score.
- To tear, rip, rend.
- Damn, drat, blast; used in oaths.
- A ration.
- Expression of annoyance or disgust; damn, darn.
- Expression of disbelief.