Or it got already taken away from NCR, and the flag is all that remains as proof of (ex-)NCR control.
Just as possible, though I suppose we won't know until it comes out. Nonetheless, it is fun to speculate.
My theory at the moment is that the main character is escaped from some Vault or military place (A7=Area 7? The government, or more specifically the enclave, was involved in the Vault-Tec project, so it wouldn't be to far fetched to believe they had their own Vault out in the desert somewhere, as a back up in case something happened to their oil rig) and is coming to NV, which is or was under NCR control. I'm certain that the player is going to be from a Vault, because it just wouldn't be Fallout if they weren't, so this fits. Plus, your character would have to be from outside NV, otherwise it would be retarded for you to be asking who or what things were.