The clenched fist [Black power salute] was very evident in the Sept. 20, 2007 Jena, Louisiana march.

But since you mentioned it, here's a link to information and a photo about the 1968 Olympics Black Power Salute:

http://en.wikipedia.org/wiki/1968_Olympics_Black_Power_Salute

Here's an excerpt of that article:

"The Black Power Salute at the 1968 Summer Olympics in Mexico is a noted civil rights protest.

Certainly one of the most overtly political statements in the 110 year history of the modern Olympic Games, Black American athletes Tommie Smith and John Carlos performed a Black Power salute at the 1968 Olympics.

After completing their 200 metre race on the evening of October 17, 1968, American athlete Smith, who won the race in a then world record time of 19.83 seconds, with Australia's Peter Norman second with a time of 20.06 seconds and American Carlos in third place with a time of 20.10 seconds, went to collect their medals at the podium. The two American athletes received their medals shoeless, but wearing black socks, to represent black poverty. [1] Smith wore a black scarf around his neck to represent black pride [2] and Carlos wore a string of beads, to commemorate black people who had been lynched.[3] All three athletes wore OPHR (Olympic Project for Human Rights) badges, after Norman expressed sympathy with their ideals. Sociologist Harry Edwards, the founder of the OPHR, had urged black athletes to boycott the games; reportedly, the actions of Smith and Carlos on October 17, 1968, were inspired by Edwards' arguments.[4]

Carlos had forgotten his black gloves, but Norman suggested that they share Smith's pair, with Smith wearing the right glove and Carlos the left. When the Star Spangled Banner played, Smith and Carlos delivered the salute with heads bowed, a gesture which became front page news around the world. As they left the podium they were booed by the crowd.[5] Smith later said "If I win, I am American, not a black American. But if I did something bad, then they would say I am a Negro. We are black and we are proud of being black. Black America will understand what we did tonight."