An architectural model.
Someone on the way to Pill Hill left behind their cardboard model of what looked like the skeleton of a pavillion, the model leaning on its side against the shelter glass.
I apologize; I didn't pick it up for TriMet Lost & Found. That's gonna be a tough one to get to Lost & Found in one piece. Plus I'm still waking up, and the morning less-coordination that hits me a bit (not as badly as some friends of mine, I know) would've made me more likely to crumple it while on the bus.