YS has 2 meanings
A pretty straightforward of telling someone you are not happy with them; may be used casually without a lot of meaning and in online gaming.
I can't believe you attacked my base right away. YS.
|OMGYS||Oh my gosh you suck|
|TRS||That really sucks|
|POMS||Peace out my sucka|
|YHS||Your hand sucks|
Might be used at the end of an e-mail or other message; also written SY, which avoids confusion with the other meaning of YS.