Rather than replacarding empty unit trains as "Residue" cars, they just leave the 1267 DOT placards on. Look at the springs on the trucks to tell if they are loads... or depending on the ruling grade the power assigned. I can tell just from the sound.
I recently spent a weekend with my old RR buddies out near Horseshoe Curve at a friend's B&B that caters to train nuts (it's a niche market, but very lucrative for the location)... a LOT of loaded CBR unit trains eastbound, an equal number of empties westbound.
I love the smell of interstate commerce in the morning.
That makes sense, too: Leaving the placards in place. Cassandra Overpass, Carney Crossing, Lilly, Gallitzin, Altoona, and beyond. I love the smell of creosote anytime.