Securities Protection Act - Declares it to be the finding of Congress that criminal dealings in marketable securities affect interstate and foreign commerce, and that such dealings are harmful to the national economy. Declares the following activities to be crimes under the criminal laws of the United States and establishes fines and prison sentences for: (1) forging or counterfeiting of marketable securities and possession thereof; (2) possession of stolen United States marketable securities; (3) theft and unlawful possession of marketable securities; and (4) use of stolen or counterfeit marketable securities at a financial institution. Defines terms used in this Act. States that the United States Secret Service shall investigate the forging and counterfeiting of marketable securities, and the possession of stolen United States marketable securities.