This feature is mainly made to properly see a bone and it's index in order to create proper mount.inc entries for your mount system!

Just select a bone and see where exactly it is. The index is shown inside the bone name list.

In this example, i want the character to be placed on the with the index of 5, so "linebeck006" and it then would look like this in mount.inc:

II_MOUNT_MNTDOUBLEBIKE01
{
	SetBindBone(5);//<--------------Bone index!
	Rotation(0.0f -85.0f -90.0f);
	SetGroundSpeed(0.40f);
	PlayerAnimation(MTI_GENFSTAND1_D);
	SetOffSet(-0.0f -0.05f 0.27f);
	Animation
	{
		"stand"		MTI_STAND
		"walk"		MTI_WALK
		"idle1"		MTI_IDLE1
		"idle1"		MTI_IDLE2
		"stand"		MTI_JUMP1
		"stand"		MTI_JUMP2
		"stand"		MTI_JUMP3
		"stand"		MTI_JUMP4
		"walk"		MTI_RUN
		"walk"		MTI_BACK
	}
}

Your mount.inc entries may look different from mine, just keep this as an example!