If you are under 10,001 lbs GVW and you do not haul HazMat (and consequently are not required to placard your vehicle), you are not considered a Commercial Motor Vehicle (CMV) under the FMCSR's, and are not required to mark or sign your vehicle.
Yea that's all true but a few states like mine consider a commercial vehicle any vehicle used for purposes of a commercial nature - meaning you are compensated for the work you are doing, you are engaged in some form of commerce. Which means that as a commercial vehicle and over 5500 GVW, you have to have signs when engaged in commerce. There is no distinction if it is interstate or intrastate work being done here and I haven't seen a change of this yet which I welcome.
The Federal DOT regulations are not the only one's being used, the states have their own requirements and agree to use the federal regulations - they are not mandated. You can ask the Feds directly how it all works, they will explain the agreement process and all of that to you.
Logging was another example, weight limits and restricted routes are still another. Just because it is under 10k doesn't mean that all the regulations on any level are not to be followed.
If this was the case, insurance companies would not require van drivers to have a CDL or some sort of professional license. The feds would not require van drivers to apply for work like a truck driver, still a 10 year history, still a medical card and still a DOT # needs to be there for interstate work, right? The CSA 2010 would not be something that would affect drivers of vans, it still does.