What does it mean to look "suspicious"?

It's a question a lot of Twitter users are asking on what would've been Trayvon Martin's 23rd birthday.

In case you need a refresher: Six years ago, Florida resident George Zimmerman — who was on local neighborhood watch duty after a string of local robberies — called the Sanford Police Department to report Martin for being "suspicious."

Martin, wearing a hooded sweatshirt, was walking home to his father's fiancee's house after buying a bag of Skittles and Arizona iced tea from a local convenience store. Minutes later, Zimmerman fatally shot him.

He was 17 years old.

Photo by Jessica McGowan/Getty Images.

Unfortunately, Martin's is just one name in a long list of young black men shot and killed after being labeled "suspicious."

As some Twitter users pointed out, it's a racial double standard that doesn't apply to his white counterparts:

But perhaps the most poignant remark in tribute to Martin's legacy came from Martin Luther King, Jr.'s daughter, Bernice.

On Feb. 5, the day after the Super Bowl, King took to Twitter to point out a troubling double standard in our reactions to mayhem erupting on the streets.

Philadelphia Eagles fans celebrated their Super Bowl victory by flipping over cars, toppling light poles, stealing trees, looting gas stations, and burning property — but despite all that violence, many media outlets brushed off these violent acts as being merely "rowdy."

Meanwhile, when civil unrest broke out in Baltimore after Gray's death in 2015, public officials, political commentators, and members of the U.S. public decried "rioting" protesters.

According to reports, cars and buildings were set on fire. The windows of local businesses were smashed and some were looted. But as King pointed out, those riots erupted out of a continuing trend of young black people being punished by extrajudicial killings and a system that fails to provide their family and communities with any justice.

Of course, the riots in Philadelphia weren't met with the same level of nationwide condemnation as the ones that took place in the aftermath of Gray's death or the verdict that set Zimmerman free.

Martin's death — and Zimmerman's eventual acquittal — helped give birth to the Black Lives Matter movement to fight against the trend of young black lives being systemically targeted and killed.

After hearing reports of the riots after the Super Bowl, Hank Newsome, president of Black Lives Matter New York, lambasted the hypocrisy in statements made to Newsweek on Jan. 5.

"Somehow, it seems there's a line drawn in the sand where destruction of property because of a sports victory is OK and acceptable in America," Newsome said. "However, if you have people who are fighting for their most basic human right, the right to live, they will be condemned."

As Twitter user @StarrburyMike suggested on Sunday evening, it's time to hold all Americans — especially those in positions of power — accountable for this racial double standard.