The deputy sheriffs civil service commission shall prescribe and enforce rules and regulations fixing the terms and conditions under which deputy sheriffs may engage in police work in addition to their normal duties as deputy sheriffs. These rules and regulations must prohibit discrimination, as far as practicable, between deputy sheriffs with regard to the allocation of additional police work. No sheriff may have a direct or indirect pecuniary interest in any outside employment. A deputy sheriff performing additional police work shall wear an identifying armband to indicate special duty.