Organization membership was open to all writers, including unpublished authors, librarians, booksellers, and other women involved with the genre.
[2] In 1997, SinC joined the Authors' Coalition of America (AC), to support international copyright distributions of members' work.
[1] In an effort to better acknowledge the diversity of SinC membership and welcoming writers of different backgrounds and identities, the organization has revised its mission statement several times to be more inclusive.
The current Sisters in Crime mission statement reads: To combat discrimination against women in the mystery field, educate publishers and the general public as to inequities in the treatment of female authors, raise the level of awareness of their contributions to the field, and promote the professional advancement of women who write mysteries.
Sitting SinC presidents have a tradition of passing down white seal stuffed animal known as "Sealine", initially purchased by former president Susan Dunlap to highlight the organization's "innovation, humor, and outspokenness" and to become a contrasting symbol for SinC's anti-corporate focus, and their goal of combatting discrimination in the genre.