27 CFR §41.74

Every package of cigarettes, except as provided in § 41.75, shall, before removal subject to internal revenue tax, have adequately imprinted thereon, or on a label securely affixed thereto, the designation “cigarettes”, the quantity of such product contained therein; and the classification for tax purposes, i.e., for small cigarettes either “small” or “Class A”, and for large cigarettes, either “large” or “Class B”.