[RightWhale]

that was not so obvious

A couple of things to look for:
An unsymmetric piece in the design that in a perfect mathematical graph wouldn't be quite like that
Crude patterns in the grass as laid down as opposed to what was left standing.

Been a draftsman for a long time. You get so you see the rough edges and don't worry so much about artistic content.

[Citizen of the Savage Nation]

That makes sense. I look for sloppiness, too, but you've got a better eye for it. These guys must be really, really good, who did #2 and #9. Regular Joes would do a half-assed job and be spotted a mile away.