"Indivisible with liberty and justice for all," the Niners said of the new flag in a statement on social media on Monday. "#BlackLivesMatter"

The new piece at the stadium is powerful ... and even star running back Tevin Coleman took the time out to acknowledge his squad's tribute, commenting raised fists on the pic.

Of course, S.F's owner, Jed York, has backed the BLM movement ever since George Floyd tragically died in late May ... pledging to donate $1 million to help fight systemic racism.

As part of the donation, York said at the time, "Before we are able to realize impactful change, we must first have the courage and compassion as human beings to come together and acknowledge the problem: black men, women and children and other oppressed minorities continue to be systemically discriminated against."

York has since given his team Juneteenth off and has insinuated he'll likely make election day in November a holiday for his employees as well.

Other 49ers players have also been vocal in their support of the BLM movement over the last few weeks ... with stud receiver Kendrick Bourne even shouting out Kaepernick while kneeling at a protest earlier this month.