When a character in the image seems to be a futanari, but it's not immediately obvious.
Signs of futanari include visible genitals/testicles, or intercourse with a stomach bulge and cum.
Whether the character is canonically a futanari or not, whether related pictures have a penis showing or not, and whether the artist clarifies that it is futanari or not aren't relevant. So long as it can't be confirmed visually, this tag can be used.
This tag might slightly overlap with futanari for the sake of usability and blacklisting, due to tags like futa with female/futa with male.