Some might believe that these are just generic teasers filled with nonsense that's meant to misdirect people, that all these "teasers" are really alluding to the general theme of "X-Base," "government testing," "etc." All of it playing into the theme you've seen in the blueprints.
Pretty sure I cracked the code, though.
The "O" is pronounced "Oh." After enough posters go up, you'll get...
"O, O, O, Oh, O..... O, O, Oh, O..... O, O, O, Oh, O.... The Right Stuff.,"
Not only is that an incredible song by Marky Mark and the Funky Bunch, but The Right Stuff is a space themed movie. Edit: Nevermind, The Right Stuff is owned by Warner Brothers so that's not it. Sorry, guys.