Zeeman splitting of one-dimensional hole subbands is investigated in quantum point contacts fabricated on a (311)-oriented GaAs-AlGaAs heterostructure. Transport measurements can determine the magnitude of the g factor, but cannot usually determine the sign. Here we use a combination of tilted fields and a unique off-diagonal element in the hole g tensor to directly detect the sign of g∗. We are able to tune not only the magnitude, but also the sign of the g factor by electrical means, which is of interest for spintronics applications. Furthermore, we show theoretically that the resulting behavior of g∗ can be explained by the momentum dependence of the spin-orbit interaction.