You didn't see it on TV or online ... but the crowd doubled down with resolve as they left the venue. It's especially meaningful because the UK government had warned -- in the wake of Saturday's London terrorist attack -- another attack was likely.

And check out the video below ... concertgoers on a tram sang the Oasis song, "Don't Look Back in Anger."

"And so, Sally can wait
She knows it's too late as we're walking on by
Her soul slides away
But don't look back in anger
I heard you say"