When assessing for vascular injury in a child who has sustained a supracondylar fracture of the femur, the nurse should look for signs of ischemia. The classic signs of ischemia, often referred to as the five 'P's, include pain, pallor, pulselessness, paresthesia, and paralysis. These symptoms indicate compromised blood flow to the affected extremity, which is a critical situation requiring prompt medical attention. Bleeding, bruising, and hemorrhage (option A) may occur due to the injury but are not specific indicators of ischemia. Increases in serum levels of creatinine, alkaline phosphatase, and aspartate transaminase (option B) are related to muscle integrity and not directly indicative of ischemia. Generalized swelling, pain, and diminished functional use with muscle rigidity and crepitus (option D) are general clinical manifestations of a fracture but do not specifically point to ischemia.