Three Plate Layouts
The 1902 Series was printed on soft porous double-line USPS watermarked paper  using three plate layouts. The 1¢ to 15¢ stamps were printed using the 400 subject plate layout shown at right. Some of the later 15¢ stamps and all of the higher denominations, the 30¢ through the $5, were printed using the 200 subject plate layout (below). The 1¢ and the 2¢ redesign were printed on 180-subject sheets to produce booklet stamps.

The 400 subject sheet was cut along both "Cut Lines" or guidelines  into four panes of 100 stamps  before distribution to post offices. The sheets were not perforated along the guidelines and straight-edges may appear on any side or even on the two adjacent sides where the guidelines intersect. Imperforate sheets of 400 were issued intact.

Each pane has two imprint and  plate markings, for a total of eight for the entire sheet. Plate Blocks may be found at all four positions, top, bottom, left and right.

The watermark orientation for these stamps is horizontal, that is in the non-rotated state as described on this page. To put it another way, the watermark may be normal or reversed or even upside down but not on its side. This is important, because early printings of the 15¢ stamp on 200 subject sheets can be told from the later 400 subject printings by this fact; the watermarks on the 200 subject printings will be on their side.  
 

The 1902 Series  400 Subject Plate Layout - 1¢ to 15¢

Which stamp is the early printing?
I can't wait ...

If you have read the left hand column you should already be able to easily determine which stamp is which. 

The early stamp, from the 200-subject plate, has perforations along its horizontal guideline. This is a dead giveaway, since stamps from the 400-subject sheets were cut, and not perforated, along both guidelines. Although it is possible a stamp may have had perforations fraudulently added along a top or bottom guideline straight-edge, this tom-foolery is unlikely to trap the knowledgeable collector. Note that the Series of 1902 stamps will never be found perforated along the left or right guideline. A stamp with such perforations has obviously been altered. By the same token, a stamp with a straight-edge along the left or right guideline does not identify a 200- or 400-subject plate layout. Only perforations along the top or bottom guideline will distinguish this.

Further separating the stamps is the difference in size. The design on the stamp on the right is clearly shorter, as well as wider, than the stamp on the left. Since the paper for the 200-subject sheets was placed in the press sideways compared to the 400-subject sheets, the grain of the paper was horizontal rather than vertical, and the shrinkage in the stamp was from top to bottom, rather than the normal left to right.

This lead to another identifying feature, the watermarks on the 200-subject sheet stamps were also sideways (sometimes referred to as "vertical"). See watermark orientations for more on this. All of the high value stamps of the 1902 Series have sideways double-line USPS watermarks.

Answer to the quiz: The stamp on the right is from the early 200-subject printing.