Is Doyles's expose the aces play legal?

[betgo]

In <u>Super System</u> he says that if there are trips on the board and someone goes allin and he had AA, he would turn the aces face up and try to read his opponent's reaction to determine if his opponent had quads or a lower boat.

This might be OK in a backroom in Texas, but I wonder if it is legal in a cardroom.

I would personally not try anything that could be interpretted as an angle shoot on an allin pot, but I am just curious.