This is a SSK. A SSK is a left slanting decrease.
Years ago, I used to have a lot of problems figuring out if a SSK was left or right slanting. Then, a teacher at some knitting event explained it so well that I have not had forgotten. The S has a \ as part of the formation of the letter. The \ slants to the left, hence SSK slants to the left. Amazing!
So the opposite would be true of K2tog. It would be a right slanting decrease because the 2 has a / as part of the formation of the number 2. And the bar in the number 2 slants to the right.
Simply amazing and I have used it ever since, just wish I could remember which teacher said that. It was worth the whole class whomever it was.