Around 3/4 in the movie Straight Outta Compton during the riots, two people are holding two scarves, one red and one blue, knit together and walking towards the police.
What's the meaning of this and/or what does it symbolise?
That scene depicts the LA Riots (related to the 4 police officers involved with the beating of Rodney King being found not guilty). The day before the riots broke out, the Bloods and the Crips declared a truce (called the Watts Truce). Many gang members would wear colors (often in the form of bandannas) to show their affiliation (Red for Bloods, Blue for Crips) so most likely the tied red and blue bandannas are to illustrate the joining together between the gangs to rebell against the L.A police force
The Watts truce is depicted I'll make this short and simple the bloods and crips were initialized as a group of men and women who protected their neighborhoods from the racist police back then if you do some research on the two gangs it will explain much more clearer why the two bandanas are tied together being held in front of the police officers