Sec. 17. TRANSFERS FROM OTHER CITY DEPARTMENTS. No prior credit shall be allowed for service to any person who may hereafter transfer from some other department in the city to the Police Department. Policemen now serving who have heretofore transferred from some other city department may be given credit for such prior service by the Pension Board. The prior-service credits shall all be granted within sixty (60) days after this Act becomes law. For example, if one is transferred from some other department of the city to the city Police Department, sixty-one (61) days after this Act becomes law, such person's service will be computed only from the day he enters the city Police Department.