Jeff,
There is maybe a five percent possibility the burn in the sign was lightning caused, but it is doubtful since the sign is directly under the power line. After a lifetime working for an electrical utility, my moneys says lightning struck the conductor above the sign burning the conductor in two and the 'live' end of the conductor fell across the grounded sign. The resulting arc burned the sign during the time the breaker/recloser/sectionalizer/fuse was operating to clear the fault which can be as short as instantaneous to ten seconds or more depending on location in the system and available fault current to operate the device.
If you happen to get back to that location, look up at the wire and see if a repair sleeve is there indicating that is where the line crew made repairs. It is an interesting photo and thanks for sharing it.