People who attack random strangers are looking for an easy victim to prey upon. Like predators in the wild, a human attacker will strike at people who look weak, helpless and unaware of their surroundings. Basically, they want an easy target that won't fight back and won't lead to them getting caught.

Since a would-be attacker doesn't know you, he or she can only judge your vulnerability based on the way you use your eyes and move your body. With a little effort and self-awareness, you can modify your body language to make it less likely that someone would identify you as an easy victim.

Eye Contact

• Casually meet the gaze of people around you. 
• Do not nervously dart your eyes at people and things around you.
• As you make eye contact, maintain your walking pace.
• Strong eye contact shows that you have self-confidence.
• It also takes away the attacker's element of surprise because he knows you have spotted him.
• If a person is following along behind you, turn around and make eye contact.

Body language

• Walk with your head high, keeping aware of your surroundings.
• Keep your shoulders rolled back.
• While walking, take long, purposeful strides.  Do not shuffle your steps.
• Keep your hands out of your pockets.  Do not fidget with anything while you walk.
• If a person invades your personal space making you uncomfortable, you should take a step away preparing yourself to react.
• Keeping eye contact, your step away should be into a 1/4 twist position, with your hands in front and your feet anchored to the ground (a.k.a. interview stance).
• Keep eye contact and stay at a distance and make space if necessary.