Verified answer

They are apart of the much longer easter egg for the Tower of Babble Achievement. Their are several of them and they are put into a table you build out in the corn field. Go to Youtube and you can look at all of this so it easier to understand. Ive built the table myself and found 4 of the 8 navcards I think. Regardless ive tried putting them into the table that asks for them and its says wrong card, I dont care much as the other way to do the easter egg is much easier. Hope this helps.