Women, how do you defend yourself in public??!?

It is no hidden secret that the world is becoming increasingly quite unsafe for women, with all sorts of unspeakable crimes committed against us..i do so want to study some sort of maritial arts(karate preferrably), but right now am hooked up with schoolwork and exams...otherwise, i always take with me some sort of bag, or an umbrella or something similar that has something painful to hit with, and is easy to swing..unfortunately, being wary of lawsuits, i can't exaclty prevent any scenes from taking place, until and unless i'm very sure that i'm in danger..while due to the grace of God, i've never had to face any such unpleasant incidents, there have been some that have shook me up, and i'd like to prevent any further occurences..even if i'm being hared, i'm sometimes hesitant to raise my voice, because somehow i feel embarred..so,what methods of self-sefence do you have in store, against a potential attacker?or how can i prepare myself against such things?