A standard disclaimer common on e.g. American coupons. A full disclaimer containing this line might read "One time use only. Valid at participating GNC stores only. No cash value. Void where prohibited, taxed or restricted by law. "(taken from a Soy coupon).
The reason that disclaimers even exist is that the US uses the British legal system, i.e. making vague laws and then letting the courts decide how they should be followed from case to case, as opposed to the French legal system, where laws are meant to be so clear that they can easily be understood and followed.