Here's some racist symbolism for you
Prof. Mark Anthony Neal has an article up at PopMatters titled The Real Nigger Show that you should read. I hesitate to excerpt it because he's more drawing a picture of a pattern than drawing attention to the specific events in the pattern.
But, of course, I'll excerpt it anyway.
Boskin notes in his book that the "minstrel show became the most popular fare throughout the country... Shuffling and drawling, crackling and dancing, wisecracking and high-stepping, the white minstrel man welded the image of the black male to material culture, laid the foundations for its entry into the electronic media of the following century, and carried it to audiences on three continents" (75-76). In other words white male performances of blackness -- faces donned with burnt cork in an attempt to "represent" the realities of black life and culture -- became one of the most popular forms of American entertainment in the 19th and early 20th century. In the absence of "real" contact with African-Americans, the minstrel stage became the site of authentic blackness for many white Americans, so much so that Mark Twain could remark in his autobiography that the minstrel stage was "the real nigger show -- the genuine nigger show -- the extravagant nigger show".
Though the minstrel stage was the most popular site for Sambo, the icon could be found in a wide array of locations including postcards, magazines, children's books (Helen Bannerman's Little Black Sambo for instance), advertisements and stereoscopic slides -- the precursor to the movie projector and television. Sambo was also presented in a variety of forms including stage performers, artifacts and athletes. According to Boskin, what all of these images shared was the intent by its purveyors to "make the black male into an object of laughter, and, conversely, to force him to devise laughter…to strip him of masculinity, dignity and self-possession." ). Boskin adds Sambo as an "illustration of humor as a device of oppression, and one of the most potent in American culture" -- an attempt to "render the black male powerless as a potential warrior, as a sexual competitor, as an economic adversary." The critical point here is though the early minstrel performances were dominated by whites in blackface, the very idea of Sambo created a context in which even black performers were forced to adhere to the conventions of minstrelsy. And of course there were rewards for such performances by blacks -- financial and social rewards that far outweighed the reality of being black and actually having to live in a Jim Crow society as opposed to performing "Jim Crow". This explains why even a light skinned black artist like Bert Williams felt compelled to "cork-up" for white mainstream audiences in the early 20th century and why some black performers continued to cork-up well into the mid-20th century.
As it happens, I agree with the description of the way Sambo was used by the mainstream, but disagree on his origin. Doesn't matter though. This piece is seriously worth the read.