Corpse marker


 * You may be looking for the novel of the same name.

A  was a [[robot] deactivation disc. They were quite often red and iridescent.  They tended to have some sort of inscription or logo on them, so as to identify their company of origin.

During one spate of murders in and around Kaldor City, they were forced into the hands of human victims. They were thus a clue the Fourth Doctor and Leela used to help solve the mystery of the murders. (PDA: Corpse Marker)