Sycamore, in the rest of the world, refers to an unrelated tree. But in the United States, sycamore is Platanus occidentalis, a fast-growing tree common to riverbanks and widespread from Canada to Texas and as far west as Iowa and Nebraska. It is even found as south as Florida. The tree is pollution tolerant, so it makes an excellent city tree and is sometimes grown for its wood.
Search for sycamores near water. They are thirsty, fast-growing trees and tend to grow near rivers, lakes and other wet areas.
Stand far back to look at the shape of the tree as a whole. Sycamores are well-branched, broad and tall and make excellent shade trees.
Use binoculars, if handy, to take a closer look at the larger trees seen from a distance in areas where sycamores thrive. The trunks of old specimens frequently reach huge dimensions.
Check for bark that is a patchwork of gray-brown flaking bark over a whitish-gray under bark. It is characteristic of sycamore trees to have bark that looks as if it was covered in thin scabs over pale flesh. (A difference in growth rates between inner and outer bark, causes outer bark to crack and flake off as the inner portion of the tree expands.)
Look for large, maple-like leaves. They can reach as much as nine inches long and broad, with three to five lobes.
Inspect the ground and tips of branches for globular, fuzzy, golden-brown fruits about one inch in diameter. When hanging from branches, they look like tiny brown Christmas ornaments. East Tennessee State University Arboretum mentions the common name Buttonball in reference to these conspicuous fruits, and says they hang all winter on the tree before dispersing their seeds in spring.
Compare your field observations with online photos and references or reputable field guides for North American trees to confirm the identification.