CEN ISO/TS 14823 "Graphic data dictionary (GDD)" is a technical specification that provides a very flexible mean to exchange complex road signs. In the perspective to extend VMS information towards vehicles (through cooperative ITS services), it seems relevant to harmonise practices between standards covering simlar topics.
The inclusion of dedicated enumeration lists for VMS pictograms (VmsDatexPictogramEnum) and additional pictograms (VmsDatexSupplementalPictogramEnum) is something rigid, not easily extendable.
Therefore, it seems preferable to replace them GDD codes and attributes. It implies to overhaul somehow the VmsMessage package.
The potential upheaval in this area made us also defer a comment raised in 2017 systematic review - to factor out the common attributes duplicated in VmsPictogram and VmsSupplementaryPictogram. We should return to consider that if that is still an issue after resolution of the GDD/pictogram code issues. The issues 191 and 192 are also related to pictogram codes.