The postcard shows an oil painting by Dizon entitled Harana. I tried to search for his/her first name, but results came up with several painters named Dizon.
I couldn't find additional information about the painting nor its location (private collection or museum).
Harana is a traditional form of courtship music in which a man woos a woman by serenading her underneath her window at night. It is widely practiced in many parts of the Philippines with a set of protocols, a code of conduct, and a specific style of music. The main instrument used for Harana is the Guitar, played by the courter, although other string instruments such as the Ukulele and less frequently, the Violin and Trumpets are also used.
Music of the Philippines: Harana Wikipedia Entry