My summary of the 6 logos seen on 3001old 2×4 bricks.
Wide logos touch the sides of the studs – narrow logos do not.
Straight O means the sides of the O are parallel. Round O means the sides of the O are convex.
I believe the Round O variants to be exclusive to Samsonite.
If you can contradict any of the information here, please let me know!
[Original post and comments on Flickr.]