Here's a look at the tattoo, which illustrates images from the civil rights and Black Lives Matter movements:
On Twitter, Stills has recently focused primarily on the nationwide protests against systemic racism and police brutality over the past month after George Floyd, a 46-year-old Black man, was killed while in Minneapolis Police custody in May.
The 28-year-old Minnesota native is among the NFL players who've taken a knee during the national anthem over the past few years to protest racial injustice and police brutality. The protest was originally started by former San Francisco 49ers quarterback Colin Kaepernick.
In January 2019, he told Cameron Wolfe of The Undefeated he understood it was a decision that could ultimately have a negative impact on his playing career.
"I'd hope it doesn't come to that. I hope my work over the last three years speaks for itself. But I've seen it happen in this league and things change," Stills said. "I'm prepared if I end up on the street and nobody signs me. I'm fine with it."
He added: "Injustice to one person is injustice to all. If they'll do that to Kap, they'll do it to any of us."