There is a widely circulated notion that certain artists, Picasso, for example, would sign their work only upon the consummation of its sale.. A great contradiction to this is Van Gogh, who painted nearly a thousand paintings, sold more or less nothing, and signed almost everything.
Van Gogh’s signature, often in lively calligraphy, is typically brightly colored and fits so harmoniously into the composition that it truly becomes integral to the painting. That is an artist signature at its best. It should blend in, not call attention to itself as a distraction, and above all, it should not become an element that might diminish the purity of the overall aesthetic intent. That issue leads to the attitudes of the twentieth century, where the rise in prominence of abstract art particularly impacted the practice of signatures.
Vincent van Gogh, Still Life: Vase with Fourteen Sunflowers, 1888, oil on canvas, National Gallery, PD and detail with Van Gogh's signature in the middle on the vase.