1304.01 Collective Membership Marks Generally 
The sole purpose of a collective membership mark is to indicate that the user of the mark is a member of a particular organization. See Constitution Party of Tex. v. Constitution Ass’n USA, 152 USPQ 443 (TTAB 1966) (holding cancellation of collective membership mark registration proper since mark was not being used to indicate membership in registrant).
Thus, membership marks are not trademarks or service marks in the ordinary sense; they are not used in business or trade, and they do not indicate commercial origin of goods or services. Registration of these marks fills the need of collective organizations who do not use the symbols of their organizations on goods or services but who still wish to protect their marks from use by others. See Ex parte Supreme Shrine of the Order of the White Shrine of Jerusalem, 109 USPQ 248 (Comm’r Pats. 1956), regarding the rationale for registration of collective membership marks.
A collective membership mark may comprise an individual letter or combination of letters, a single word or combination of words, a design alone, a name or nickname, or other matter that identifies the collective organization or indicates its purpose. A membership mark may, but need not, include the term "member" or the equivalent.
In addition to the mark being printed (the most common form), a membership mark may consist of an object, such as a flag, or may be a part of articles of jewelry, such as lapel pins or rings. See TMEP §§1304.02(a)(i) and 1304.02(a)(i)(C) regarding use of membership marks and acceptable specimens.
Nothing in the Trademark Act prohibits the use of the same mark as a membership mark by members and, also, as a trademark or a service mark by the parent organization, but the same mark may not be used both as a membership mark and as a certification mark. 37 C.F.R. §2.45(f); TMEP §1306.04(f).
See TMEP §1302.01 regarding the history of collective membership marks.