Weak semi-circular mark in bottom left corner

a

No mark in top left corner

Weak mark in top left corner - no mark in top right corner

a

Double mark left of center of bottom ridge

a

Line at 10-o'clock of stud 4

Mark in bottom left corner

a

Marks above slot on right edge

a

a

Mark between studs 2, 3, 6 and 7

a

Marks on both sides of bottom slot

No marks on top side of brick

No mark on bottom ridge

b

No line at 10-o'clock of stud 4