Hirschfeld is known for hiding his daughter Nina's name in most of the drawings he produced after her birth in 1945. The name would appear in a sleeve, in a hairdo, or somewhere in the background. As Margo Feiden described it, Hirschfeld engaged in the “harmless insanity,” as he called it, of hiding her name [Nina] at least once in each of his drawings. The number of NINAs concealed is shown by an Arabic numeral to the right of his signature. Generally, if no number is to be found, either NINA appears once or the drawing was executed before she was born.