I've conferred with Jake and we like this direction!
One thought is if 99 should be Irrigation Signage, or if it's there just to stay out of the way of everything else and might have a better separate location. Calling things "99" is the best indicator that maybe it doesn't really match perfectly with everything else in the folder.

Should it definitely be here, and not under 10-14 Signage? I know for convenience, in the irrigation folder is great, but we also don't account for "keep off the grass" signs in 32-92 Turf and Grasses, or in other folders. I'm leaning towards just one common location for signs for the master categories (and add a folder for irrigation signs in there), and firms like your own can override that decision and add a secondary signage folder in any other folders they choose.

-Amanda