This article is from the Paper Money Collecting FAQ, by Bruce Giese firstname.lastname@example.org with numerous contributions by others.
On the front side, the black seal to the left of the portrait is the
Federal Reserve Seal and Letter. The green seal to the right is the U.S.
Treasury Seal. The four black numbers near the corners are Federal
Reserve Numbers. See section 3.14 for a list of Federal Reserve Banks
and their numbers and letters.
The design on the $1 bill is the Great Seal of the United States
of America, whose design was set by act of Congress, June 20, 1782.
In short, the pyramid is a Freemason emblem, the eye in the triangle
is a symbol of God, the motto "annuit coeptis" is usually translated
as "he hath smiled on our undertakings", and "novus ordo seclorum"
means "a new order of centuries".
According to a government pamphlet, the Unfinished Pyramid stands
for "permanence and strength." It is unfinished to symbolize the
"future growth and goal of perfection" of the U.S. The All-Seeing Eye
stands for a "deity." The 13 stars overhead, 13 vertical stripes in the
shield, 13 olive leaves, and 13 arrows all represent the original 13
The various little numbers and letters on the front and back are
check letters, face plate letters, quadrant numbers, and back plate
numbers. They are used to identify the printing plates and the position
of the note on the plate. These items vary--see section 2.7.
The date on the base of the pyramid is 1776 in Roman numerals.
The right-hand side roundel shows the coat of arms of the US:
the 13 stars above the Eagle's head represent "a new constellation
in the firmament of nations" according to the 1782 text.
Here is the text (the language is supposed to be heraldic language,
though it is in fact poor quality):
The device for an armorial achievement, and reverse, of the great seal
of the Unites States in congress assembled, is as follows:
ARMS: Paleways of 13 pieces, argent and gules; a chief, azure; the
"escutcheon on the breast of the American eagle displayed proper, holding
in its dexter talon an olive branch, and in his sinister a bundle of
13 arrows, all proper, in his beak a scroll, inscribed with this
motto: E pluribus unum.
For the CREST: over the head of the eagle, which
appears above the escutcheon, a glory, or, breaking through a cloud,
proper, and surrounding 13 stars, forming a constellation argent
on an azure field.
REVERSE: A pyramid unfinished. In the senith an eye in a triangle,
surrounded by a glory, proper. Over the eye theses words: Annuit
coeptis. On the base of the pyramid the numerical letters,
MDCCLXXVI. And underneath, the following motto: Novus ordo seclorum."