That sign is called 'bunny-ears', but it doesn't suggest any kind of foolishness. People do it in photos, just to make the victim look silly. (Anyway, I don't see shy it looks like a dunce's cap - the angles are wrong.)
PS You may come across the term 'foolscap' in old sources. Most people in English-speaking countries (except the USA ) use the A-series of paper sizes. A4 is the nearest to foolscap, but it's shorter and wider. But I only mention this because 'foolscap' was so called because when first produced it had as a watermark a fool's cap.