I've found a cheap way to mount your FROG plate or FMCA or whatever on your rear ladder....
Instead of paying $25.00+ for a holder from CW, go to local hardware an get a rural mailbox plate that you sit a mailbox on an use it - $6.00... Works great... Looks great....
Ernest; I see where you are using white nylon zip ties to attach the sign. UV will turn them brittle in about a year and your sign will blow away. I suggest that you use the black UV resistant variety and use two for each attachment as a safety precaution.
Nice idea - but just a suggestion. Why not use the standard nuts and bolts that are used to mount the plate to the holder as you would on a vehicle. You could do away with the tie wraps entirely.