A cracked frame.
Broken rear derailleur hanger (ways around that... but is it worth it?)
Crease in the top tube or downtube, just behind the head tube (indicative of front-end damage).
Bent fork... can be replaced, but look for other signs of damage (as above).

NEEDS A FORKLIFT TO MOVE IT AROUND. Lots of good Columbus tubing, Reynolds 531, and butted chromoly frames around. No need to get a basic High-Ten straight tube frame.

For touring, consider tire clearance and perhaps also rack mount points.