Q: "Nobody who can channel saidin or saidar can sense the True Power. And, since the Forsaken don't seem to notice Moridin channeling the True Power, is it detectable at all (besides by a gholam)? That is, can someone already holding the True Power sense another using it?"
RJ: "No. Not by any method we've seen yet."

You can apparently design a ter'angreal to sense the TP at least. After all, the True Power was also sensed by those, who later drilled the Bore. But normally, as the others said, you can't sense the TP.