American Society for the Prevention of Cruelty to Animals, New York, named Rawle Murdy, Charleston, S.C., for a new assignment, to help market its A.S.P.C.A. Collection pet products at Wal-Mart stores. Spending has not been determined. Rawle Murdy came to the attention of the organization for a campaign the agency created last year for the Charleston Animal Society, styled as a mock election between a dog named Spike and a cat named Biscuit.