How do you know you have been spotted on bfbc2?

I know you press the back button to spot someone, but is there a way of knowing if you have been spotted by the enemy?

I sometimes hear the narrator say something like "there's an enemy sniper", does this mean you have been spotted or just they have a sniper in the team?How do you know you have been spotted on bfbc2?
Here's a sign you have been sighted. You're either getting shot at, or your dead.How do you know you have been spotted on bfbc2?
you cant because thats gonna help you out over the enemy, and lol yeah i think the first answer kinda says it all