It is a bellyband:

a band of paper around a new book, usually printed with information about the book's contents and sometimes used instead of a book jacket.

(Dictionary.com)

a band that is used as packaging or decoration around a book, magazine, or similar item.

(Merriam Webster)

(rhollick.wordpress.com)

(www.pinterest.it)

wrap-around band

A paper strip wrapped around a book like a dust jacket, but smaller in height than the book. It is typically used for promotional purposes and may be added post-publication .**..

From: wrap-around band in The Oxford Companion to the Book

Subjects: Literature — Bibliography

The Oxford Companion to the Book

The same would go for the notebooks in the question.

paper bands

Or, less fancy, just paper bands:

extrapackaging.com/bands

I would have called this an obi (on Wiktionary as “A strip of paper looped around a book or other product”). But this is possibly just jargon relating to the paper strips included with CDs and games imported from Japan where the word originates.

wrapper noun the cover,
1)usually of paper or cellophane, in which something is wrapped
2)a dust jacket of a book

dictionary

Just because the wrapper has got very small and less wasteful, that is what it is, the wrapper holding 3 books together.

And in a sentence

Just take that little wrapper off the books so we can get started.