Which is the common format for indicating in-text endnotes and footnotes

MLA format.

Explanation:

Endnotes and footnotes in MLA format are indicated in-text by superscript Arabic numbers after the punctuation of the phrase or clause to which the note refers: Some have argued that such an investigation would be fruitless.

Thesis: The author of this letter to the editor makes an analogy to the famous "I Have a Dream" speech by Dr Martin Luther King in the structure and organization of the essay. They use metaphors like " their words were bullets" and "fire back to the protesters" in order to convey the message that the protests they encountered were painful and doing damage to her best friend.  The author also opens with a vignette describing their encounter with the protesters.  

Explanation:

A vignette is a small impressionistic scene or small descriptive passage often used at the beginning of a piece of writing that sets a scene or describes an example the writer analyzes to get their point across to the reader.  The vignette the author of this letter uses gives a lot of detail about the protesters and what their signs and shouts were saying. A metaphor is a figure of speech likening something to an object or action that is not literally applicable. In this case, the words were not guns but the author likened them to bullets.  An analogy was made to the famous speech by MLK in the overall structure and organization of the essay to compare her friend's desire for a better life to the "American Dream" notion that the United States is the land of opportunity.