This building was another one that stood in the 600 block of DeSiard Street, right at the corner of 6th:
https://www.louisianadigitallibrary.org/islandora/object/lsu-sc-p16313coll52%3A1162
I am guessing that window is where African-American clientele picked up their prescriptions, since they were not allowed under Jim Crow laws to enter the whites only front entrance. I am not sure though. This is just an educated guess.
Ouachita Parish History Tidbits 