Vigilance, common sense, as Mimitabby said, and, I would add, confidence and assertiveness.

This applies more to walking than cycling, but I always walk with a purpose, looking ahead, back straight and proud shoulders. Even when I am lost in a foreign city where I don't know the language or in a shady part of a strange town. I don't want to be in a situation where someone feels justified to offer me help; however I will go get help myself before it's too late (and will make sure I am never in a situation where I am vulnerable to good samaritans, like I will always have the capacity to fix my own flats).

If someone talks to me, I always talk back with a confident voice or if I choose to ignore this person (which I wouldn't do except in specific circumstances I think), I do it with pride and confidence, too. Smiling (rather than being snotty/*****y) facilitates firmness and assertiveness and fends off many problems. And I keep going at my purpose (i.e. keep walking), not getting distracted and staying aware of my body, belongings and surroundings.

It might be by sheer chance that I never had problems, but I have put myself in what others would consider potentially dangerous situations in the past (like walking out in a strange city by myself in the middle of the night), have encountered shady strangers and had conversations with some of them, and have always courteously walked out of every situations. No physical constraints were ever applied to me. This, again, could be sheer luck. But I tend to believe that if I don't look and act like a prey (or, worse, an easy prey), I will not be picked by predators.

So if a sniper wants to shoot me off my bike while I ride of course that might happen. But I won't stop riding (or doing anything else, for that matter) for potential predators out there.