Matchbox sign is a psychiatric

Psychiatry

Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

 symptom. Patients with delusional parasitosis

Delusional parasitosis

Delusional parasitosis is a form of psychosis whose victims acquire a strong delusional belief that they are infested with parasites, whereas in reality no such parasites are present...

 often present at the doctor's office with what MDs term the "matchbox sign", a medical sign

Medical sign

A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....

 characterized by the patient making collections of fibers and other foreign objects supposedly retrieved from the skin. The name refers to the fact that such collections can be stored in matchbox

Matchbox

A matchbox is a box made of cardboard or thin wood designed to hold matches. It usually has a coarse striking surface on one edge for lighting the matches contained inside....

es or other similar small containers, which are then presented to the patient's physician.