The standard symbol to represent a hard disk in the I.T world is a cylinder that, I guess, resembles a can.
That's the reason that a little "can" (or cylinder) is customarily used to represent the hard disk on the face of computer cases. A led (or light emitter of some sort) was added to indicate hard disk activity.
The reason a cylinder was chosen is because each platter of a hard drive is logically divided into concentric tracks. A set of tracks, each on a different platter, at the same distance from the center, forms a logical cylinder. It is from this fact that the cylinder became representative of a DASD (Direct Access Storage Device - formal name) or more commonly called a hard drive or hard disk.
HTH.
Edited for typos.