I have notice that in the last week or so that security in the RER stations has been stepped up. I commute through the largest station in Paris (Les Halles, which also includes an underground shopping mall) and I have been seeing fire teams of 3 soldiers armed with FAMAS assault rifles casually patrolling in both common areas and track side. These guys are lean and fit. They walk with their rifles slung diagonally across their chest with the barrel pointed down, their right hand is on the grip with trigger finger ready for action. Sometimes I see them deployed in a triangle formation to cover more area but still support each other. When they stop someone for questioning, usually two of them will question the person of interest while the third stands back and provides over watch. They seem to be mostly in transportation zones as I don't see them in the tourist areas, including the Metro stations.
Strangely, I do not feel threatened by this show of professionalism and firepower.