The smoke effect to enhance the design.
No one has likely thought to tattoo just smoke, as that would be quite strange. However, adding a smoke trail to a tattoo is a well-known technique. Well-tattooed smoke looks visually appealing, as demonstrated by tattoos of candles with thick clouds of smoke. Don't forget about designs that depict a man or woman (silhouette or portrait) smoking a cigarette. A lit cigarette without visible smoke looks rather weak. Such tattoos are popular in black ink, and most of them are in this style.
