A radiologic sign resembles a specific object, often suggesting a group of similar pathologies. These types of similarities are useful to increase awareness and shorten the list of differential diagnoses. As in other fields of radiology, in obstetric ultrasonography many signs have been described to ease diagnosing. These signs identified on prenatal ultrasonography include the lemon and banana signs observed in spina bifida, teardrop sign in corpus callosum agenesis, keyhole sign in Dandy-Walker syndrome and posterior urethral valve, double bubble sign in duodenal atresia, rabbit lip in cleft lip cases, and in extremity anomalies, frog leg sign in caudal regression syndrome and sandal gap sign. The 2- and 3-dimensional ultrasound images of cases with these signs accompanied by the objects they resemble are presented in this review.