As far as I know, the sign in OKC only says something like "On this site stood the Alfred P Murrah Federal Building, site of the second worst terrorism attack on US soil."
I've not been to OKC in quite some time (despite being born there).

2 years ago, when the signs came down, they said something like (and i'm paraphrasing here, it's been 2 years)
"We hoped we would never have to change these signs, and especially not in our lifetimes."