I appreciate the review; got a couple of nice emails on this also. Never occurred to me to use the LAC call numbers, but their own system seems rather chaotic - I see one set of numbers attached to the photos published online, and then another set of numbers when photos are used in books. Having experienced first hand their cataloging system, I think frustration is built into the system.
As you already noted, the book is devoted solely to NW Europe, so no UK or Italian signs, which indeed would be interesting. If a decent source of such images presents itself, I am sure an enterprising author out in the world may find suitable inspiration in this book to attempt a follow up. I see there are people here suggesting retirement projects for you...though like my dad, sounds like your retirement will consist of full time employment.
Anyway, thanks all for the comments, I'm pleased with the way the book has turned out.