Two purple horizontal lines on a white background
This button is most likely supporting a feminist or LGBT cause.
Purple was one of a trifecta of colors used by the Women’s Suffrage and Political Union in England at the turn of 20th century. The colors were brought to the United States suffrage movement by women who had worked for British suffrage. The three colors—purple, white, and gold—originally symbolized loyalty, purity, and hope, and have remained symbolic to the modern-day feminist movement. The equals sign with regard to feminism is a statement indicating that women should be equal to men.
Since the mid-1990s, the equals sign has become primarily associated with the LGBT rights movement. This is in large part due to the Human Rights Campaign—an LGBT advocacy group—who adopted the symbol as its logo in 1995. Lavender, similar to the color of the equals sign on this button, has also been historically associated with lesbian rights.