At many cafes or popular eateries you will see a sign asking the public not to 'study'. This particular sign implies that you could study between midnight and 6 am if you wish!
Students often study for hours at these places, so employers are obviously getting sick of it.
There is also a joke here: you can leave your wallet or cellphone lying around and it will be safe - but don't ever leave your study notes. The notes will get stolen!