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.
