Male sugar gliders have a distinct bald spot on the top of their head that appears as they reach sexual maturity (the age of this is variable, but often around 12-15 months of age for males). This area, which is a diamond-shaped patch right on the forehead, is actually a scent gland. The male glider uses this scent gland to mark his female mate, his offspring, and his territory.
The male sugar glider actually has three scent glands: the one on his head, a second on his chest (which may appear as a small bald spot or may cause the fur to be slightly discolored in the area over the scent gland), and a third in the genital area (next to the cloaca).
The female has scent glands in the genital area as well as in the pouch. Sugar gliders have a fairly mild odor, described as a sweet musky smell. While it may be a little stronger in the male at breeding season, it is not a strong or offensive odor.
A small photo of a male showing the bald spot can be found on this page about sugar glider anatomy.