I just picked up on this on another forum and thought I would pass it along. Bear in mind this is for a commercial vehicle.
Per FMCSA reg 393.11(d), Prohibition on the use of auxiliary lamps that supplement the identification lamps. No commercial motor vehicle may be equipped with lamps that are in a horizontal line with the required identification lamps unless those lamps are required by this regulation.
In other words, those who like extra "chicken lights" across the top of their trailer will be in violation.
I realize this is more applicable to the folks who pull a trailer behind their toter involved in commercial activities. But, in the interest of staying more "invisiable", it might be useful info.
PS, at present, there is no limit on additional vertical lighting on the rear.