This is a small, tiny thing. Just a circle that you draw on the top right corner of a piece of paper that your teacher hands out in class. It can be a circle about the size of a dime, or a nickel, that's all.
What the circle means, when it's empty, is that whatever is on that page will be due sometime, one day soon. It also means that you need to fill in that deadline or due date. So the empty circle sits there as a reminder that you need to write in the due date, and then you need to do the assignment, and after that you need to turn it in.
We get a blizzard of paper every day, all day. Pages and pages. My AP Psych teacher says we get so many in that class because our textbook is so out of date that she has to add all the rest of the information we need by passing out all these papers. She also tries to save paper by putting different stuff on the back side of a lot of the papers, so it's easy to miss that an assignment is on the back that has nothing to do with what's on the front.
The problem is that some of all these papers are just for you to read, and some of them are for you to actually do something with. What makes it even worse is that some of the papers LOOK like they are assignments, but the teacher says they aren't, and some other papers look like things to just read but the teacher assigns something you're supposed to do with what you read.
So your best friend is that circle. And it works best if you can try to make a habit of asking right when you get the paper: is this read only, or when is it due?
Better to be the one who asks all those questions than get a zero.