In doing volume forensics it is exceedingly rare to find a full volume of random data and when one is found one can be fairly certain that someone is using TrueCrypt or had a lot of time on their hands when destroying evidence by using dd to write dev/random to disk. Depending on the technical capacity of the forensics lab this observation could be sufficient enough evidence in itself to back additional search warrants or court orders. Remember, it is absolutely possible to stand out simply by being off the curve of normal, whether when using HD encryption or anonymizing services.