When they try to make sense of Eve/Juliette's scratchings in the tunnel wall, Monroe points out they have signs, symbols and letters in a variety of different languages and scripts before exclaiming that they need their own Rosetta stone for it. The Rosetta stone was the key to deciphering the ancient Egyptian scripts because it contained the same text in three different languages. It makes no sense for Monroe not to see the parallel here - the symbols could actually be "their own Rosetta stone" if they signify the same thing in different code systems.