Above the gray concrete of Union Square and crowds of tourists scrambling about it, you perceive, after a moment, the eyes of Colin Kaepernick.

The eyes of Kaepernick are gray and solemn — their irises multiple stories high. They look out over Union Square in the city where the former San Francisco 49ers quarterback was once athletic royalty.

Now, the unsigned Kaepernick is an activist — and the face of a new, controversial Nike "Just Do It" campaign. His image graces a newly erected billboard atop the Nike store in Union Square.

"Believe in something. Even if it means sacrificing everything," reads the text scrawled across a black-and-white photograph of Kaepernick's peaceful face. A minuscule "Just Do It" and Nike swoosh logo hover over his stubbled chin.

The Nike campaign references the movement Kaepernick sparked among athletes after he began taking a knee during the national anthem to protest police brutality. He is currently involved in a lawsuit with the National Football League, accusing the organization of blacklisting him.

Kaepernick announced the endorsement on Monday by Twitter. The backlash followed thereafter, with some angry consumers posting photos of themselves burning their Nike gear in protest of the company's use of the divisive figure.

Nike apparently sees the risk of alienating conservatives and Donald Trump supporters as paling in comparison to a Kaepernick endorsement, who is one of the most talked-about athletes of the moment.

"The long-term relationship and a contract that benefits both parties over the next 10 years will likely outweigh any current controversy," said Bloomberg Intelligence analyst Chen Grazutis.

President Trump took time on Tuesday to comment on the ads.

"I think it's a terrible message they're sending and the purpose of them doing it, maybe there's a reason for them doing it," he told the Daily Caller. "But I think as far as sending a message, I think it's a terrible message and a message that shouldn't be sent. There's no reason for it."

The San Francisco billboard is in good company in Union Square. The giant visage of Kaepernick stares across the way upon the gentle, boyish likeness of a multiple-stories high Harry Styles. Adjacent to Kap, also in black-and-white, is a billboard that shows a man seemingly frustrated by his laptop. Between the monochrome duo is an advertisement for Sierra Nevada beer. "Enjoy outdoors," it reads.

Read Michelle Robertson's latest stories and send her news tips at mrobertson@sfchronicle.com.

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