Green’s Dictionary of Slang

(US black drugs) an extra-long marijuana cigarette.

1972		E. Folb Urban Black Argot 145: Stencils long, thin marijuana cigarettes.
1977		J.L. Dillard Lex. Black Eng. 96: Folb’s study of urban argot showed that ‘only three of eleven marijuana items were known exclusively by Black subjects’: gunny, skoofer, and stencil.
1980		E. Folb Runnin’ Down Some Lines 171: Or could roll one o’ dem stencils. They out-grown joints. Lotta weed – I mean long! Joint ’bout five papers rolled up.