The first Friday of June is National Gun Violence Awareness Day, and to mark the occasion, activists across the country are wearing orange to honor victims and survivors of gun violence. Among the celebrities speaking out about gun violence on Friday was former President Barack Obama, who noted in a tweet that last week's Virginia Beach mass shooting was just one example of the "senseless gun violence" that plagues the country. Obama's National Gun Violence Awareness Day tweet also called on Americans to make a pledge "to protect lives."

"Last week, it was Virginia Beach," Obama tweeted. "But day after day and year after year, too many families and communities are shattered by senseless gun violence. We can't get numb to this. On National Gun Violence Awareness Day, pledge to speak out, #WearOrange — and vote — to protect lives."

According to the Chicago Sun-Times, the Wear Orange campaign was launched in 2013 after 15-year-old Hadiya Pendleton was shot and killed in Chicago. Following her death, her friends and family wore orange to generate awareness about gun violence, and to honor Pendleton. Pendleton was not far from Obama's home in Chicago's Kenwood neighborhood at the time of the shooting, and she was killed just one week after she performed at his second inauguration, CNN reported.

In the years since Pendleton's death, the Wear Orange campaign has taken off across the country. On Friday, lawmakers like Massachusetts Sen. Elizabeth Warren and South Bend Mayor Pete Buttigieg, both of whom are running for president in 2020, joined Obama and other prominent politicians in urging people to wear orange.

But that's not all Obama wants Americans to do. In his tweet, Obama urged Americans to speak out and vote — a message echoed by New York Sen. Kirsten Gillibrand, who in a separate tweet urged elected officials to "stand up to the NRA."

According to the Wear Orange campaign's official website, an average of 100 Americans are killed with guns each day. There have been 159 mass shootings this year alone, per the Gun Violence Archive, killing or injuring more than 1,400 children and teenagers.

In order to commemorate National Gun Violence Awareness Day, hundreds of cities will host nearly 750 events over the weekend, Newsweek reported. In honor of this annual event, which was first recognized in 2015, activists and anti-gun violence groups organize marches and awareness events nationwide on the first Friday of June.

This year, a wide range of lawmakers, celebrities, corporate brands, and other organizations are participating in National Gun Violence Awareness Day, as well as in the Wear Orange campaign. According to Newsweek, comedian Samantha Bee, actress Julianne Moore, and companies like Levi Strauss and Penguin Random House have all pledged their support to the Wear Orange campaign.

However, it looks like President Donald Trump won't be joining any National Gun Violence Awareness Day events. Although the president published several tweets on Friday about Vice President Mike Pence's birthday and about traveling back to the United States from his trip to Europe, he made no mention of gun violence.

Instead, he called on Democrats to put forward a "good and solid immigration bill" and suggested that the moon was part of Mars. Although Trump previously suggested that he would push for a few gun control measures following last year's school shooting in Parkland, Florida, he quickly reverted to NRA-supported policies like arming teachers and increasing school security, Reuters reported.