The director of finance may invest moneys held for the police relief and retirement fund in the types of investment provided for pensions under the Annotated Code of Maryland, 1957, article 73b, section 13 (1); provided, that moneys of the police relief and retirement fund shall be invested in other than United States treasury and federal agency securities only upon approval by a majority of the police relief and retirement fund advisory board. (Mont. Co. Code 1965, § 18-21.)