We owe the drawing of the Tshirt design and the 2004 contest
logo to professor James Oxley from LSU Math Department.
It portrays a finite projective plane of order 3 which consists
of 13 points.
Projective Geometry is a geometry that is different from
the usual Euclidean Geometry students learn in high school.
In Plane Euclidean Geometry, two points determine a line
and each two lines either intersect in a point or are
parallel. Given a line and a point not on the line there
is exactly one line parallel through the point. In Plane
Projective Geometry, two points determine a line and each
two lines intersect in a point. A finite Projective Plane
is a Plane Projective Geometry with a finite number of
points and lines. The one that appears on the Tshirt
has 13 points and 13 lines. There are several spots that
look like lines cross, but they do not. The only intersections
are at the numbered bold points. The other crossings are
only there because the schematic picture was drawn on
an ordinary plane.
More information about projective planes may be found
e.g. at
http://en.wikipedia.org/wiki/Projective_plane
For a fascinating story please see The
Search for a Finite Projective Plane of Order 10
This can also be read in the American
Mathematical Monthly volume 98, 1991, pages 305 
318.
