One obvious indication are his low vocals on the live performances. I have both the Heavy Left-Handed and Candid DVD as well as Live Bait For The Dead, and it's the same in both cases. His "growls" live nowhere near approach the death vocal effect that they do on countless songs. Also, if you have not noticed, on his high shrieks, his voice always begins to waver/shake live. This never happens on the studio releases; the note is always steady. Point is, the variation of his live vocals nowhere near approach what they do in the studio; the only explanation for this that he isn't able to vary them as much, which in turn leads to the conclusion that he uses effects in the studio.