Brazil The 100th Birthday of Violeta Parra November 21, 2017 Violeta Parra (1917 - 1967) was a Chilean composer and songwriter. She reinvented Chilean folk music and extend its sphere of influence to Latin America. The commemorate stamp shows a photograph of Violeta Parra playing a guitar.
The one Boliviano value of the country's 1987 "Musical Instruments of Bolivia" set shows three charangos. According to Wikipedia, "The charango is a small Andean stringed instrument of the lute family which probably originated in the Quechua and Aymara populations in the post-colonial times".
In May and June of 2005 Spain issued two computer-vended stamps (Michel #s 160-1) featuring paintings by contemporary artist Paco Melendez Torres. Both of these of paintings depict a guitar among other still life objects.
On February 18, 1988 Norway issued set of two stamps to commemorate the centenary of the Salvation Army in the country. The lower value 2.90 kr. stamp (Facit #1026) depicts a Salvation Army Band, including a guitar player.