Who remembers being surprised to see "Directory Art" after you typed:
LOAD "$", 8
LIST
Instead of a boring list of filenames and block counts, the entire directory screen transformed into a beautiful piece of directory art (dir art / d/art). The surprise hit hard the first time you saw it on a cracked game disk; I was like, "What just happened?!"
The drive's "directory" isn't a normal file — when you ask for "$" (the special filename meaning "show directory"), the drive generates a fake BASIC program on the fly.
The first two bytes are the load address (like any PRG file), then it spits out tokenized BASIC lines: line numbers (those 18, 40, etc.), the block counts as "PRINT" statements, filenames in quotes, file types like PRG or DEL, and finally "107 BLOCKS FREE." and "READY." as the last "lines."
Normally this just looks like a messy program listing when you LIST it.
But clever sceners realized: "Hey, we can overwrite those 'lines' with PETSCII block characters (like the diamond borders, checker patterns, hearts, etc.) while keeping the structure intact so the drive still thinks it's a valid directory."
They used deleted files (type DEL) or carefully placed dummy entries to draw in the 16-column filename area, turning the directory into ASCII/PETSCII art.
When this popped up on your C64, it was amazing. Who remembers seeing directory art on their Commodore 64?