Symbol Schema Tree Metal Sign

About the Schema Tree design

Four identical rectangles, each a heavy frame around a wider-than-tall opening, hold the whole design. Three stack down the left edge with short vertical bars between them, and the fourth steps out to the right on a stub that meets the middle one at its waist. Nothing curves anywhere, and every connecting bar is exactly as thick as the frames it touches, so they read as hallways between rooms rather than wires.