  We devise tests for a new physics origin of the recently measured direct CP
violation in singly Cabibbo suppressed D decays. The tests take the form of sum
rules for the CP asymmetries in various D decays. They are based on the fact
that within the standard model CP violation arises from interference of the
dominant tree amplitudes with the Delta I=1/2 penguin amplitudes. The sum rules
would be violated if the observed CP violation is due to new physics
contributions to the effective weak Hamiltonian that change isospin by Delta
I=3/2.
