Look around the area where you found the seed to find the source tree. A windmill palm is a medium sized palm that matures between 20 and 40 feet high. It has a slender, fibrous trunk that is 8 to 10 inches in diameter. In older trees, the fiber may slough away and expose a smooth, ringed surface. The windmill palm will have palmate leaves, which means the leaves look like a fan.
Once you have identified the source tree, take a look around to see if there are other seeds. If the seeds are brown with two distinct round hemispheres and a rounded pea shape, chances are high that they are windmill palm seeds.
Climb a ladder and harvest some of the ripe fruit off a windmill palm if possible. The fruit will have an oblong appearance and be bluish in color. They will be around 1.2 centimeters in diameter. The "true" seed will be under this fruit. Finding these bluish fruits is an almost definite sign you have found windmill palm seeds.