What is the 1870 button lawmakers were wearing during the State of the Union? We explain.

President Biden delivered his second State of the Union address Tuesday night, speaking to a full House chamber packed with senators, representatives, and Supreme Court justices. Eagle-eyed viewers might have noticed a number of congressmembers sporting buttons printed with the year 1870.

Over time the State of the Union has become a venue for lawmakers to make a point with their apparel. During the Donald Trump years, for example, many female members in the Democratic caucus wore white as a tribute to early suffragists and a continued commitment to women's rights.

Smaller statement pieces like buttons are also a common appearance. Last night Sen. Elizabeth Warren (D-Mass.), along with a few others, donned a crayon shaped pin in her lapel, representing the importance of federal investment in childcare.

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What is the 1870 pin's meaning?

Many members of the Congressional Black Caucus, along with some other Democrats, wore 1870 pins as a way to spotlight the need for policing reform.

The year 1870 is the first on record when a free, unarmed Black man was killed by police. In March of 1870, Philadelphia police chased down and shot Henry Truman in an alleyway.

The pins were distributed by Rep. Bonnie Watson Coleman (D-N.J.), who said in a statement on Twitter: "153 years later the Black community is still waiting for justice."

The buttons served as a poignant reminder of the lives that continue to be lost to police violence, made all the more searing by the presence of Tyre Nichols' family in the audience. Nichols, who was killed by Memphis police officers weeks ago, was mentioned by name during President Biden's address. "Something good has to come of this," Biden said, quoting Nichols' mother RowVaughn Wells.

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This article originally appeared on USA TODAY: What happened in 1870? Why lawmakers wore the State of the Union pin