Earthen jugs formerly used in public house for drawing ale: they had the figure of a man with a large beard stamped on them; whence probably they took the name: see BEN JONSON'S PLAYS, BARTHOLOMEW FAIR, &c. &c. Dutch earthen jugs, used for smuggling gin on the coasts of Essex and Suffolk, are at this time called grey beards.
GREY BEARD
Meaning of GREY BEARD in English
Slang English vocab. Английский сленговый словарь. 2012