In the absence of cryptanalysis, the output of a symetric cipher looks like random bytes. Every one should have a hardware RNG on their computer. "I am sorry your honor, that is a file of random numbers that I was using to check the output of my RNG." Or "I am sorry your honor that is a one-time pad I was planning to use."
But, would the average jury understand what a RNG is? The prosecution would probably argue that "It's a tool used by terrorists and child pornographers so that they can create 'codes' to communicate with each other". If they say that, they could probably even supress any explaination of what a RNG actually is, by claiming that it's "to dangerous to allow into public record". The Phrack E911 document was supressed in that way. In some countries I could see people being charged with an offence just for having a RNG... The output looks encrypted, and I heard that in France (and other countries) it is illegal to create anything that even *looks* encrypted. :( Disclaimer: IANAL