The person in question was just somebody with a weakness for industrial architecture.
The "no cameras" signs were very popular in east block countries. It was forbidden to take pictures of bridges, government buildings, airports, railway stations, industrial installations, water dams etc. The signs were prominently displayed and the consensus on their purpose was essentially to scare and comfort the sheeple. There was an interview somewhere in early 90-ties when ex-government employee attested to that. The counter-intelligence purpose was irrelevant even then - it was just too easy to hide cameras. But harassment of tourists and hobbyists was great PR, proof that 'authorities' are doing the job and disarming the imminent evil. In a depressingly predictable manner US of A is sliding into the same mode of operation. And, depressingly, it works. Expect more manufactured everyday threats, more citizen-informants, the works. Contracting or subcontracting airborne demolition artists is not practical on ongoing basis ... we need a terrorist threat everywhere, every day. Make sure your children do not overhear your non-compliant conversations.