Stop Wasteful Advertising by the Government Act or the SWAG Act This bill prohibits the use of federal funds for publicity, propaganda, swag, or mascots, with exceptions. Swag is a tangible product or merchandise distributed at no cost with the sole purpose of advertising or promoting an agency, organization, or program. Each agency shall, as part of the annual budget justification submitted to Congress, report on the public relations and advertising spending of the agency for the preceding fiscal year, which may include an estimate of the return on investment for the agency. The prohibition pertaining to swag shall not apply to an agency program that supports the mission and objectives of the agency that is initiating the public relations or advertising spending if the spending generates a positive return on investment for the agency.