Then, per Geneva Conventions, we are required to notify that we are not going to honor those requirements. And frankly, the little protection we get from them is far better than letting any of our good men and women be treated a whit worse than they are by the enemy. If we announced the freedom to execute prisoners, it would be far worse a loss to us than to our foes.
Of course, one could argue that our snipers do not meet the clearly visible insignia requirements, etc., too...so be careful what you ask for.
Treat our people any worse than they are? Every person who is captured by the terrorists are beheaded with a dull knife, not even given the benefit of a swift beheading with a sword. How on earth do you think they could treat them any worse?
Given that snipers are never popular with the enemy, it's pretty unlikely that a sniper will allow himself to be taken alive. Those 2 snipers in Mogudishu went down fighting. It would be an unusual circumstance if a sniper were captured, so I don't know the situation/dilemma you are alluding to would ever really occur.