It seems that you are overthinking this a bit.

A nondescript backpack or vehicle is a good idea because it makes you look like everone else. It really doesn't help a criminal to know that a wise prepper will use a plain backpack, because he still can't tell the BOB from all the others packed with DVD collections and ipods.

I would hope that normal response (if any) to education about preparedness would be to consider preparing, not "Thanks! Now I know who to rob in an emergency."