When used of time, the abbreviation P.M. means this "meridiem"
The only universally accepted American abbreviations are "a.m." and "p.m." ... 
OWL (APA/MLA) [4]: 9 p.m. or 9 P.M.; New York Times Manual of Style and 
Usage [5]: 9 p.m. (uppercase only ... What means abbreviation M.E.?