It is like his political symbol which he used during his presidential campaign for the 2015 presidential election and he used it again at his swearing in ceremony on May 29, 2015.
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The raised right fist salute was the symbolic Black Power salute of the African American civil rights movement in the 1960s and became very popular among revolutionary groups in the Americas, Africa and other parts of the world. Feminist movements also use it.
The great Madiba Nelson Mandela of South Africa used it until he passed on. The never-say-die Robert Mugabe of Zimbabwe has been using it since the days of guerilla warfare against racist Rhodesian government under Ian Smith.
History of the Raised Fist
The raised fist salute consists of raising one arm in the air with a clenched fist. The meaning can vary based on context.
Different movements sometimes use different terms to describe the raised fist salute: amongst communists and socialists, it is sometimes called the red salute, whereas amongst black rights activists, especially in the United States it has been called the Black Power salute. During the Spanish Civil War, it was sometimes known as the anti-fascist salute.
The Victory of Muhammadu Buhari and the Nigerian Dream by Michael Chima Ekenyerengozi (Paperback)