Battle's sign, also known as mastoid ecchymosis, is a late indication of fracture of middle cranial fossa of the skull, appearing as bruising over one or both of the mastoid processes at least one day after the injury. Such fractures can be associated with underlying brain trauma, as they appear as a result of extravasation of blood along the path of the posterior auricular artery. The sign is named after William Henry Battle.

Battle's sign is considered a late sign, as it takes at least one day to appear after the initial traumatic basilar skull fracture, similar to raccoon eyes. Battle's sign may be confused with a spreading hematoma from a fracture of the mandibular condyle, which is a less serious injury.