Tap Code (Not The Larry Craig Kind)?

Greg Allen looks at campaign imagery from McCain Blogette, Meghan McCain's blog. Allen comments:

I'm still trying to decide who made this sign, though. It's "M-C-C-A-I-N" spelled out in tap code, a cipher used by prisoners in solitary confinement. It puts the letters into a 5x5 grid [minus the K]. So M is third row, second column, etc. This sign, in other words, says "JOHN MCCAIN, POW." I can't figure out if it was printed by the campaign and handed out, or if this guy just happened to make it himself. [It doesn't have the two-color printing of the official McCain signs, and the blue is slightly off. But would a random guy put at otherwise meaningless star on the top, and the campaign URL?] Whether it's supposed to telegraph McCain's POW bona fides to a knowing audience, or whether it's meant to imply that McCain's POW experience somehow qualifies him for the presidency, the relentless playing of the POW card seems beyond the pale.