Early Chinese bronze seals for official use often had long handles which made it easier for the user to stamp them repeatedly in the course of their paperwork.
Of course, other shapes are common, like those shown below. Both of these have shorter “handles” with holes in them for attaching a cord to make them more convenient for carrying suspended from your belt or perhaps around your neck.
Since the Ming dynasty, when scholars found they could carve their own seals from soft stone, these handles have mostly disappeared, at least with seals for private use. In fact, the shape for a scholar’s seal stone has been reduced to that of a handle—a long rectangle.
For more on the different styles and shapes of these handles see the page on seal knobs.