The best guess now is that the object departing columbia on flight day 2 was
a hunk out of the left RCC panel 8, maybe half a foot across or more.

Suppose it had shown up on an exterior PLB camera view, flashing off near
the horizon.

Would it have looked really different from 'ordinary' debris, different
enough to be a recognizable symptom of something worth worrying about?

If so, does this imply future shuttle flights should keep a better eye
outside?

JimO