§ 920. Alphabetical indices in offices of county clerks. The clerk of each of the counties within the city of New York, so long as he deems it expedient, may continue the alphabetical indices of the parties to notices of lis pendens, statutory notice of liens and claims upon land, or of the parties to either of them, and of the owners of land against which liens have been filed and of judgment debtors whose names appear on record. The particular form of such alphabetical indices shall be as such county clerk shall determine, and shall be certified by him as having been prepared under the authority of this article. Such indices shall be kept in the office of the county clerk or in such other place as shall be provided for them and shall be public records.