eyebrow windows (the things small windows above the main windows). Md 80s have 'em, 100s don't. also, fokker 100 have long flap actuator housings while the md-80 has the ghetto-riffic dc-9 style ones. also, all AA md-80s seem to have black radoms, except the ex-reno air ones, which are all white, not silver, and the TWA ones, which, well, still say TWA.
When in doubt, one B pump off