This Signature value represents the PD signature. This variable is valid only while a PD is detected. In 802.3af and 802.3at standards the power controller on the PSE uses two of the four pairs of wires in the RJ45 connector to supply power to a power controller on the PD. With 802.3bt standard the controller on the PSE uses all four pairs. On the PD side there can either be single power controller, or two distinct power controllers connected to each of the two pairs and each of the two controllers would negotiate and draw power independently from the PSE. The Controller on the PSE is capable of detecting the PD signature, which will indicate whether the PD comprises a single controller or two independent controllers. Possible values: unknownSignature : 2-pair mode, singleSignature : 4-pair mode and one controller on the PD side, dualSignature : 4-pair mode and two controllers on the PD side.