You have a .38 M & P 4th change, serial number 575193 would have been manufactured circa 1927. Valuation independent of the Springfield Police Department marking would be $300 to $400. With additional research, that would add a premium. I would start with a factory letter and then an inquiry to the Smith & Wesson Historical Foundation as to what the Star, which means this revolver went back to the factory, means as far as additional factory work performed.