People's Liberation Army of South Vietnam was the official name of armed forces of the Communist-organized Republic of South Vietnam under the Viet Cong. Its flag was derived from the Viet Cong flag by adding the words "Quyết thắng" ("Determined to win") in the top hoist, as used in the flag of Vietnam People's Army. A reconstruction of this flag, using a modern typeface, can be seen here: https://www.ttxva.net/luoc-thuat-co-quan-su-viet-nam.
While numerous photos of hand-made Viet Cong flag bearing this inscription, which occupies different positions along the top edge, can be found by any image searching of the Web, a black and white photo of the flag with correctly positioned text, in a rather peculiar typeface, can be found here https://www.flickr.com/photos/13476480@N07/3771046133. Since the photo was taken at an official event, it proves that the displayed layout of charges was official. Tomislav Todorovic, 12 November 2015