1. What does it mean?
ㅅㄱ abbreviates 수고. After a shared task or game it can mean 'good work' or a casual 'see you,' drawing on longer expressions such as 수고했어.
Also written or said as su-go
2. The nuance
It can also sound dismissive, especially after an argument or a competitive win. It is not a universal polite equivalent of 'thank you'; use a fuller expression with unfamiliar people.
3. Examples
“자료 같이 정리하느라 ㅅㄱ. 이제 쉬자.”
Good work sorting those materials together. Let's take a break.
“오늘 연습 다들 ㅅㄱ, 다음 주에 봐.”
Good work at practice today, everyone. See you next week.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.