Go on Word or Pages or whatever you have, and type the name of your class so that it just fits on your page.
Print it out, and cut it out so that it's smaller to work with.
Once it's the "right" size, place the paper on your notebook the way that you think is best.

Now go imprint the word(s) onto you notebook using a pencil or pen or w/e.

Go over the imprint with a cool colour and you're done! I did it with pencil first, to see how it'd look...
Now you'll never take the wrong notebook to class again :)