Green’s Dictionary of Slang

Spanish guitar n.

(US) a cigar.

1934		H.N. Rose Thes. Sl.
1944		Maurer & Baker ‘“Aus.” Rhyming Argot’ in AS XIX:3.
1949		Monteleone Criminal Sl. (rev. edn).
1969		S.T. Kendall Up the Frog 20: ’E offers me one of ’is Harry Wraggs, but I sees ’e ’as a Spanish Guitar on ’isself.
1979		Maledicta III:2 172: Spanish guitar n Cigar; rhyming slang.