I’ve got to share what I just found about gtk-doc.  I’ve been using it for months now to document libchamplain’s API.  It was complex to setup but the result is worth it.  Here is my experience about how to get your properties and signals to show up:

• Is my_object_get_type listing in the .types file?
• Is the section correctly identified in your doc and -docs.sgml?
• And today’s discovery: is your object struct declared as a typedef?

To make that last point explicit:

typedef struct
{
  GObject parent;
} MyObject;

will produce minimalistic documentation while

typedef struct _MyObject MyObject;

struct _MyObject
{
  GObject parent;
};

will produce complete documentation with properties, signals and object hierarchy.

Consider yourself warned!