This stamp may have a rectangular grill pattern impressed into the back of the stamp. These patterns vary in their dimensions, each different dimension receive a classification. These are "A Grill' ''B grill' etc.

The dimension of the grills are as follows
A grill: covers entire stamp (only 9 copies known)
F Grill: 9mm x 13mm, 11-12 points x 15-17 points.