Some notes are simple and to the point: "Naomi, please look for my special note to you in the living room. T.F."
The motivation behind others is harder to decipher. Like this scrap:
"Whereas John is manipulative and cruel so he is not good enough for the throne, now therefore I proclaim myself to be the rightful heir to the throne."
Was it a game? Homework? Someone genuinely upset?
McKellar likes "to do" lists. She pulls out her favorite.
"It's just such a great list of things," she says. "It includes 'Vegas,' 'getting unemployment?' and 'Lucky Brand jeans.' "
One thing she's noticed over the years is that many of the notes appear to be written by kids.
"I think the main thing (that) says," McKellar says, "is that kids are probably far more likely to leave behind things that they aren't meant to leave behind. So many little pieces of homework."
"Go home now!" reads one scrap in shaky script. "Please don't say funny words," reads another. "Barack Obama is hard-working because he has to make new laws, speeches and take care of his family." says a third.
Nina Lindsay, the supervising librarian for Children's Services at Oakland Public Library, keeps her own collection on the walls of her office.
One of her favorites is a ransom note written by a child to the whole world: "Dear World, Each citizen needs to give 100 dollars so each country, state, citizen, should at least have a thousand dollars."
Lindsay adds that the ransom note was accompanied by "a lot of pieces of fake money, just different scraps of paper, like fake Monopoly money, so it made me hopeful that the ransom was being paid.".
Lindsay says the notes are precious as windows into another world.
"Children usually are used to talking to adults in the way they think they are supposed to talk to adults," she says. "And I feel like we don't always get to hear what's going on in their minds and hearts, and these notes let us see inside that a little bit."
McKellar says some of what she thinks is appealing about the notes, and has made them a hit on the blog, is the fact there is a bit of mystery around them.
"I feel like in general the things you find in a book, it's one of two things. Either it's a throwaway thing, you either needed a piece of paper to mark your place," says McKellar. "Or else it's something that's so intimate and personal that you want it with you, and you want to carry it with you everywhere you go, so it becomes a part of this thing you’re reading every day. And they are so different from each other it's interesting to try to figure out which it might be."
She reads some of the more sentimental notes in her collection:
"Remember I love you sweetheart. The past is the past. So let's not take it home with us. I just want to love you and be happy."
And: "I hope when you find this, whatever you are doing, you are having a great time."
She says she dreams of reconnecting some of the notes, photos and drawings with the people who make them.