"Let me give you an O"

I picked up Collin from school.  When we got inside the house, he gave Burke a hug first as usual.  I was in the kitchen making Collin a snack when he came over to me and said, "Let me give you an O".  Yeah, I know.  What's an O?  What creative game is he making up now?  I asked, "What's an O?"  He said, "I'll show you" and then gave me a hug.  He then asked me to bend down so he could give me an X.  You guessed it....and X was a kiss.  I love Collin's X's and O's.

Later, I read an email from the teacher which did explain how he knew about X's and O's.  Because Valentine's Day is this Friday, they are learning about friendships, Valentines and, apparently X's and O's.