I found a photograph online showing a young woman sitting in front of two flags at a municipal expo. The two flags are the Dominican Republic national flag, and the other I take as the municipal flag of San Francisco de Macorís since that is the booth where the photo was taken. The flag appears to feature the city coat of arms of San Francisco de Macorís on a white field. I was able to confirm that the coat of arms is, in fact, that of the city in question, so I feel fairly confident in the assessment of it as a municipal flag. Randy Young, 19 December 2015
San Francisco de Macorís is the capital of the Dominican Republic's Duarte province. Located in the north central part of the country, San Francisco de Macorís is the eighth largest city in the Dominican Republic. The name of the city comes from a combination of Saint Francis (members of the Franciscan Order came from Italy to this area during colonization) and the territory's original name, Macorix.
Source: Wikipedia article Randy Young, 19 December 2015