An abstract stylized representation of the vulva hand-gesture (sometimes also known as the "Yoni sign" or "Yoni mudra"), used particularly among some lesbians and feminist spirituality advocates.  Occasionally done with the thumbs below, but the version with the thumbs upwards (depicted here) has a stronger symbolic resemblance.  The American Sign Language sign for "vagina" makes use of the same positioning of the hands.
See https://www.thoughtco.com/mudra-photo-gallery-4051990 ("yoni mudra"), https://web.archive.org/web/20160310115219/http://www.lesbischleben.de/englwissenlexikon.htm ("lesbian hands"), The Woman's Dictionary of Symbols and Sacred Objects by Barbara G. Walker (ISBN 0-06-250923-3) p. 332 ("yoni sign"), the cover of the November 15-21, 2007 issue of Time Out New York  (ASL sign), etc.
This highly simplified depiction (using black-and-white silhouettes only) shows the thumbs and index fingers just as they are about to touch.  If they are forcefully pressed against each other, then the resulting handsign will be narrower and slightly taller.  If the thumbs are not bent, and touch each other right at their tips, then the resulting hand-sign will be broader and more triangular...
This also appears in James Branch Cabell's classic novel Jurgen: "Anaïtis placed together the tips of her thumbs and of her fingers, so that her hands made an open triangle; and waited thus", in an obviously symbolically sexual context ("her gauzy tunic had twenty-two openings, so as to admit all imaginable caresses... And now Jurgen shifted the red point of the lance, so that it rested in the open triangle made by the fingers of Anaïtis", etc.).

Apparently a more traditional Indic yoni mudra is a more complicated hand gesture, with palms upwards and fingers of the two hands intertwined.
Own work
AnonMoos