Yikes. Written permission for professional photography?
I had thought ‘professional’ meant something like ‘earning a living from’. But the definition in the OED also includes having the skill of someone that is a competent professional. I suspect that the sign is meant to convey that no
commercial
photography is allowed without written permission, either that or it could be more clearly written as
only incompetent photography allowed.
But, just to be on the safe side, I wrote myself a note giving myself permission to photograph before proceeding to do so.