New York Consolidated Laws, Not-For-Profit Corporation Law - NPC § 501. Stock and shares prohibited;  membership certificates authorized

A corporation shall not have stock or shares or certificates for stock or for shares, but may issue non-transferable membership certificates or cards to evidence membership, whether or not connected with any financial contribution to the corporation, as provided in section 601 (Members).  The fact that the corporation is a not-for-profit corporation, and that the membership certificate or card is non-transferable shall be noted conspicuously on the face or back of each such certificate or card.