The affidavit of any disinterested person as to posting notifications required for the sale of any real estate to be sold by the sheriff or his deputy, constable or tax collector, in the execution of his office, may be used in evidence in any trial to prove the fact of notice, if such affidavit, made on one of the original advertisements, or on a copy of it, is filed in the registry of the county where the real estate lies, within 6 months.