IT is one of the earliest pieces of police memorabilia relating to the pay and conditions of police. In December 1872, the following edict, headed ''Volunteers for Duty in Hong Kong'', was issued. ''The superintendents will submit by first despatch bag, 9th, a list of single men, properly qualified, willing to proceed to Hong Kong. ''The constables selected must be of good character, of at least three years' service, under 32 years of age, of fair height, and good constitution. ''The pay of the constables is fixed at 40 dollars, equal to nine pounds a month, and the men selected will have to enter into an agreement binding them to serve for a period of five years; an annual supply of clothing and free quarters will be provided. ''A free passage will also be given and the expenses of each man paid to the place of embarkation. ''The men selected will have the option of renewing their engagements at the expiry of the term for which they agree to enter, or of being sent home at the public expense. ''A pension, at the expiration of 10 years, at the rate of a quarter of the annual salary, and an addition of one 60th of such annual salary will be granted.''