I don't know the name, but by Googling around I got the idea that Sarco might be a variant of Zarco (or vica-versa of course), and sure enough, on this site about Spanish-origin family names there is an entry for "sarco, zarco":
http://www.nmgs.org/artfilgl.htm
Zarco is a Spanish word, with a meaning of "light blue" or similar:
http://es.wiktionary.org/wiki/zarco