Is It P.S.S. Or P.P.S.?

Earlier today, I was helping my nephew with a birthday card he was making for his grandpa on his dad's side of the family. He drew the picture, and I wrote the message (though he came up with the words). We had the main message, and then we added a P.S. message. Then, he wanted to add what he called a "P.S.S." message. I told him it was called "P.P.S." (only for him to laugh over the "P.P." part).  To be sure, I looked it up. I was right. It is P.P.S. Not that I've had much cause to use it that I can recall.

Even earlier today, I did what will likely be my last load of laundry before I go home. Only four or five days left until then.