I stand still get my phone out and ask the turnip in arabic or english if he would like to talk to my husband. then i flip open the camera bit and say police and try and take a picture. I don't shout - just calmly but firmly. works every time
if they are in a car i say i have your number i can go to the police.
if it isn't serious i just sneer and look at them like the microbe they are.
however if i am walking locally i really dress down. baggy clothes - that cover. then i can't be accused of sending out 'the wrong messages'
however i think asain and black ladies get more grief than i do.