As for the original poster, you never know what someone has been through. The lady could have been robbed before or just intimidated by your presence, who knows. I tend to think there is a difference between racism and prejudice and I'd say what you dealt with was prejudice, its not different than the Arab man that people keep their eye on at the airport or the Mexican that is assumed to live here illegally. It is certainly wrong but the response is dependent on the individual, some turn the cheek and others speak up.

It doesn't seem like you're bothered too much by what happened so I wont go all into it. But when someone tells you that you need to change your appearance to be accepted, it is them who needs to change the way they think rather than you changing how you carry yourself, especially as it pertains to dreads which I consider to be cultural.