Smoke is a slur used to describe Blacks in a derogatory way. From the similarity between their skin color and the color of smoke. Also from the way that they were said to be able to sneak around quietly, entering a room "like smoke".
The word Smoke is a racial slur that has been used historically to degrade and dehumanize blacks. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to blacks. If you are unsure about whether or not it is appropriate to use the word Smoke, it is best to err on the side of caution and avoid using it in any situation.