What are those? I am glad you asked.
If they ever feel the need to talk to me about the book (by having a reading conference -- read more about that here), they can move their card to the "Let's talk about my book" section and I will immediately call a conference with the student (of course I will also talk about books in passing with the students but this is a bit more formal of a discussion....actual time set aside.)
Once the students have finished the book they are reading, they will erase the title from their card and fill in a book spine to add to our classroom "bookshelf" (which you can read about more in detail here.) After they have chosen a new book to read, they will write that on their laminated card and the cycle continues.
What I am finding is also happening with this, besides just me knowing what the kids are reading, is that the other students in the class also can see what is being read. They are using this as an opportunity to check out a new book they might have previously not looked at. Since their classmate is reading it, it must be good, right? Students are also seeing that the series' that they are reading are also being read by others. It has sparked some nice conversation between my students about which books to read.
How do you keep track of the books students are currently reading during silent or at home reading time?