The implication of this Metafilter post is that someone is providing soldiers with pre-written letters which they simply sign and send to newspapers. Or, according to this article, someone is signing the letters for them.
This kind of thing has been nicknamed astroturf — i.e., a fake grassroots. The Republican Party is fairly fond of it.
I think it’s more than usually repugnant when it’s used to misrepresent what our soldiers think, however. The men dying in Iraq deserve better than to have their views hijacked by a public relations flack.