First, I want to thank all of you for your replies. Very helpful and enlightening. I'd also like to comment on some of them.
In my area, as I may have mentioned, the relationship between inspectors and sign companies is relatively new. I believe my first inspection was in the early 80's. NRTL listing was not required until the late 80's. It's true that a listed sign means that only field wiring should need inspecting. It's also true that an awful lot of listed custom neon signs are never seen by a UL inspector, and, as Larry said, "Neon has always held some mystery for inspectors. Sign installers have taken advantage of this...." I've had my share of inspectors confess to a job being his first neon inspection. (Correct me if I'm wrong, but I imagine most inspectors are electricians, and most electricians are not real familiar with NEC 600, UL48, and the foreign looking equipment and accessories in a neon job.) It's true that not all UL companies will roll the dice on whether the UL inspector is going to show up for a spot inspection, and not all installers will take advantage of an inspector who may not be up to snuff on a neon installation. "I have a hard time believing the sign companies are sneaking all that much past UL." And, "Anybody can be a UL shop. Sign the agreement and order your labels." Send the check, I might add. For these reasons, it's my view that these signs should be inspected a little more closely by field inspectors, at least until they're satisfied that the contractors and fabricators in their area are aware that, odds are, corner cutting and the like are not going to go unnoticed, and at the same time the inspectors are educating themselves on the machinations of neon systems.
"It sounds like you should blow a whistle, for the public's sake." I did, on a particular service call, take pics, record infractions, inform the owner of my safety concerns, and email both the pics and my records to UL. I know the owner did nothing. I never heard from UL. I wasn't aware that there is a proper procedure to follow, and I may not have followed it.
"If you (the inspector) look at a channel letter sign and rely on the label, you are taking a chance. " I realize most inspectors already have a full plate at the beginning of each day. But taking a little more time is better than taking that chance, IMO.
On a side note in response to something Larry said, "A lot of installers have complaints about the GFP transformers. Tripping out where the old non-GFP type would not. I would not put it past some installers to replace with old style XFMRS or somehow defeat the GFP. Defeating it would be hard as it appears to be all encapsulated." While not being a thing of the past, spurious
tripping of the SGFP is at an acceptable low level; that is, if the installers realize that a little more care, and sometimes different procedures, than what was once necessary must be taken when wiring these types of transformers. Finding the old style (not made for use in the USA, Canada, or most Euro countries), I think, would be harder than wiring the system correctly in the first place.