Batman and James Gordon went to the spot where Pete Savage was killed. Gordon was looking at the photos, while Batman was checking out the rat maze:
Batman: More symbols. It's another cipher.
James Gordon: He blasted these out after his message went viral. Bastard murders you and your reputation.
Batman: That guy pushes drops. On the east end.
What does "drops" mean?
If a word is unusual or unfamiliar in the context used, and it's something related to crime or police work, it's usually a drug reference.
"Drops" was the name given to a narcotic used in Gotham City. Initially produced by the Maroni Organization, the drug was manufactured by the Falcone Crime Syndicate after Don Salvatore's arrest. By Batman's second year, drops were believed to be causing widely spread consequences across the city and efforts were being made to combat its influence. Addicts to drops were commonly referred to as "drop heads".
They likely have that name since they're administered like eye drops, dripped onto the surface of the eye.
'Drops' are a fictional addictive drug sold in Gotham City. Addicts (known as 'dropheads') administer the drugs via an eyedropper, hence the name.
He lifts AN ENVELOPE OF CASH off the tray -- Batman watches him hand the Woman A RUBBER-BANDED CLUSTER OF VIALS WITH EYE-DROPPERS -- a.k.a. "DROPS" -- the Woman turns to go, but stops, struck, as she sees THE PHOTO - her eyes briefly meet Batman's -- then she heads out --
[...]
... A GROUP OF DROPS ADDICTS SPRAWLED on melted metal bed frames, FACES CONTORTED IN FROZEN GRINS; one GIGGLES in a daze -- Gordon swings his light to the Figure from the hallway, who cowers, gripping A BOTTLE AND EYE-DROPPER --
GORDON: Friggin' dropheads ...
etc.
Fictional drugs are often used in films and TV shows to allow the makers to show representations of drug use without being accused of demonising (or glamorising) specific kinds of drug users.
