Three equally separated nonorthogonal quantum bits that lie on the same plane are prepared for signal processing. One of the qubits is randomly picked as the single-qubit signal. The remaining two qubits then form the two-qubit signal. We find that the optimal probability operator measure for the two-qubit signals can be interpreted as the optimal orthogonal measurement in the four-dimensional Hilbert space of the signal states. We also find that the two-qubit signals have a better detection probability than the single-qubit. Possible generalization to the case of N nonorthogonal qubits is also discussed.