Unfortunately...
...but confirmed by multiple sources, the parts of the "Patriot" Act that empower Feds to place taps on ISPs include gag provisions to prevent the ISP from telling anybody about it. The tap would indeed be classified.
We could work out a code ahead of time. How about this? If I ever start to espouse Creationism or ID, that's the signal that my system's been compromised. Or that I've suffered a head injury and lost the use of at least half my brain. Either way I'm hosed.