The sniper in the story decides to smoke the cigarette at the end of paragraph 3 and smokes it in paragraph 4.  The action could be symbolic of a couple of things.  Being a sniper is a solitary profession.  Even if the sniper has a spotter, he/she is working with only 1 other person.  In this story, the sniper is working by himself.  He is a prime example of a "lone wolf," and readers are told that he is good at his job when we read that he is used to seeing death.  We assume it is the death of somebody at the other end of his scope. 

By having the sniper smoke the cigarette and risk exposure, the author could be trying to further deepen the character's hardcore and fierce persona.  He knows that it is a risk to smoke the cigarette, yet he decides to take that risk for no other reason than his own pleasure.  That's hardcore.

The cigarette smoking could also symbolize that the sniper has gotten to the point that he simply doesn't care anymore.  He has seen so much death and destruction that he is becoming jaded by it all.  He wants to live but knows that isn't likely to happen, so he figures why deny himself simple pleasures.  He's not being brave by smoking the cigarette; he simply just doesn't care anymore.

Finally, the cigarette smoking could symbolize his confidence in his skills.  He's not being tough by smoking the cigarette, and he isn't displaying a carpe diem attitude.  The sniper thinks about smoking the cigarette before he smokes it.  He knows that it is dangerous, but he decides to take the risk.  He is confident in his location and his hide.  Unfortunately, he is spotted by an enemy sniper and wounded; however, even while wounded, the sniper maintains cold logical precision and thinks of a way to outwit his enemy.