Green’s Dictionary of Slang

bob n.5

[abbr. bobo n.2 ]
(drugs)

(also brown bob) a marijuana cigarette.

[US]College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 Bob (noun) A blunt twisted already. [Ibid.] Brown Bob (noun) A blunt without the weed.
[NZ]D. Looser ‘Boob Jargon’ in NZEJ 13 28: bob n. Marijuana.