Juveniles tend to go for that bizarre puncture additions thing for display purposes, usually an attempt to appear ‘unique’.
So possibly some odd placards could be misappropriated by juvenile dragons for this purpose.
Side story?
Parallel story perhaps - Might be distracting from the main course - of people getting ate instead of eating.
Point of view of the dragon(s) doing the eating perhaps - not the people in the story trying to “tame”/accommodate the dragons?
Back to the parallel teenage dragons getting metalled by the DOT: if on a trailer or dump truck going down the highway, would a dragon be like a dog (wanting to hand his head over the side with his tongue hanging out? Or like a cat: Supremely uninterested in the whole thing, but demanding his own upholstered seat and lap blanket?
Or a gecko or Gila monster. Hard to see either as anything but “Lumpish.” Which doesn’t fit the “juvenile delinquent dragons wearing heavy metal” image.