We have an etymologist amongst us.
[QUOTE=OldSalt93;5721328]To have a monkey on one's back may be considered a metaphor that means to have a terrible burden that one can not get rid of, to grapple with a problem that will not go away. Often, to have a monkey on one's back means to have an addiction that one can not control, or to be addicted to drugs or suffering withdrawal from a drug addiction. The origin of this idiom may be the stories of Sinbad, the earliest known works are from the seventeenth century. In one story, a creature described somewhat like an ape jumps on Sinbad's back and will not get off. However, an older story attributed to Aesop involves a dolphin giving a monkey a ride through the water. The idioms monkey on the roof and monkey up the chimney meant one had a mortgage to pay, in the late 1800's. Having a monkey on one's back in the 1800's meant to be angry. Later, having a monkey on one's back came to mean having a terrible burden. In the 1930's the idiom was applied to a drug addiction, particularly heroin. Sometimes the phrase is expressed as get the monkey off one's back, meaning to rid oneself of a burden, problem or addiction.
In the context of this forum, "signs of a monkey" generally mean signs of drug addiction, whether that be paraphernalia lying about, skin problems associated with drug use (scabs, sores, etc.), physical behaviors such as twitching (tweaking), slurred or extremely rapid speech. Or needle / track marks.[/QUOTE]While I knew the current meaning, I didn't know the etymology of the expression. John Ciardi would be proud of you.
Credit where credit is due
[QUOTE=BareBackJack;5721467]While I knew the current meaning, I didn't know the etymology of the expression. John Ciardi would be proud of you.[/QUOTE]I take no credit for the first paragraph. It was a straight up copy and paste from a Google search result. I will take credit for already knowing the etymology, but someone else did all the work of composing it into the precise and concise paragraph I shared.