The correct answer is: A. Buttonhole sign.
With application of gentle pressure, a neurofibroma will easily invaginate into the subcutis, a finding known as the buttonhole sign.
This question asks the examinee to identify neurofibromas by multiple soft, rubbery, skin colored to pink-tan papulonodules, and apply their knowledge of classic skin physical exam signs. When pressed on gently, a neurofibroma will invaginate into the subcutis, demonstrating the so-called buttonhole sign (choice 1). The dimple sign (choice 2) refers to the downward movement of a dermatofibroma when it is pinched. Crowe’s sign (choice 3) is axillary freckling seen in neurofibromatosis type I; it is not a feature of the neurofibromas themselves. Darier’s sign (choice 4) is local urtication with rubbing of lesions of cutaneous mastocytosis, while the pseudo-Darier’s sign (choice 5) is transient induration occurring with rubbing of a smooth muscle hamartoma.
Madke B, Nayak C. Eponymous signs in dermatology. Indian Dermatol Online J. 2012 Sep-Dec; 3(3): 159–165.