Brown was eighteen years old. In the NBC News tweet about the story, the network chose a photo of an unsmiling Brown standing outside of a nondescript building, wearing a basketball jersey.
In the photo, Brown is making what looks to me like a straightforward peace sign with his left hand. Some online commenters interpreted the hand gesture as a 'gang sign.'
@NBCNews THAT HAPPENS TO BE A GANG MEMBER SIGN!!— bufordisaacs (@bufordisaacs) August 10, 2014
The police say that Brown struggled with a cop over the gun. Brown's family is very skeptical, as is the larger African-American community in Ferguson. A photo can be an argument, and the photo NBC News chose made a different argument than a more typical victim photo (at a graduation, or at home) would have. In response, people of color began tweeting pairs of photos of themselves under the hashtag #IfTheyGunnedMeDown.
Among other things, this is what social media in general, and Twitter in particular, is good at. It's hard to talk through the semiotics of an NBC News social media editor's photo choice. You can spend a long, bogged-down time using words to parse pictures. It's easier, clearer, and more powerful to see that argument made with just a few words and a couple of pictures.