Interesting. If I were to create a TrueCrypt container with a goal of keeping it undiscovered, I would:

1. Do what I said a couple posts up - name it something seemingly-system related and put it in a Windows system folder, or in a program's folder.

2. Obviously, do not give it the TrueCrypt standard ".tc" extension.

3. Keep the container file size small. The only legitimate multi-GB system files are page files.

4. Be sure to clear the recent files and apps list in Windows, and be sure that TC doesn't keep track of which containers you've opened recently.

5. Use TC's plausible deniability ability: create a second encrypted container inside the original one, with some "secret-looking" files within the first container but not the second one. This is just in case the other person manages to find the outer container file in the first place.

But really, there's no way for anyone to say that a given file is a TC container: TC will try to decrypt any file you give it. The only way to know for certain that a file is an encrypted container is a) for it to be one and b) to give the correct passphrase to decrypt it.