public static void SetGameObjectIcon(GameObject go, string texturePath)
{
	Texture2D texture = AssetDatabase.LoadAssetAtPath<Texture2D>(texturePath);

	if (texture == null)
	{
		Debug.LogError("Couldn't find an icon...");
		return;
	}

	var so = new SerializedObject(go);
	var iconProperty = so.FindProperty("m_Icon");
	iconProperty.objectReferenceValue = texture;
	so.ApplyModifiedProperties();
}

public static void SetGameObjectIcon(GameObject go, EditorIconType iconType)
{
	Texture2D texture = EditorGUIUtility.FindTexture(GetIconPath(iconType));

	if (texture == null)
	{
		Debug.LogError("Couldn't find an icon...");
		return;
	}

	var so = new SerializedObject(go);
	var iconProperty = so.FindProperty("m_Icon");
	iconProperty.objectReferenceValue = texture;
	so.ApplyModifiedProperties();
}

public enum EditorIconType
{
	GreyLabel,
	BlueLabel,
	CyanLabel,
	GreenLabel,
	YellowLabel,
	OrangeLabel,
	RedLabel,
	PinkLabel,
	GreyRound,
	BlueRound,
	CyanRound,
	GreenRound,
	YellowRound,
	OrangeRound,
	RedRound,
	PinkRound,
	GreyDiamond,
	BlueDiamond,
	CyanDiamond,
	GreenDiamond,
	YellowDiamond,
	OrangeDiamond,
	RedDiamond,
	PinkDiamond
}

private static string GetIconPath(EditorIconType iconType)
{
	switch (iconType)
	{
		case EditorIconType.GreyLabel: return "sv_label_0";
		case EditorIconType.BlueLabel: return "sv_label_1";
		case EditorIconType.CyanLabel: return "sv_label_2";
		case EditorIconType.GreenLabel: return "sv_label_3";
		case EditorIconType.YellowLabel: return "sv_label_4";
		case EditorIconType.OrangeLabel: return "sv_label_5";
		case EditorIconType.RedLabel: return "sv_label_6";
		case EditorIconType.PinkLabel: return "sv_label_7";
		case EditorIconType.GreyRound: return "sv_icon_dot0_pix16_gizmo";
		case EditorIconType.BlueRound: return "sv_icon_dot1_pix16_gizmo";
		case EditorIconType.CyanRound: return "sv_icon_dot2_pix16_gizmo";
		case EditorIconType.GreenRound: return "sv_icon_dot3_pix16_gizmo";
		case EditorIconType.YellowRound: return "sv_icon_dot4_pix16_gizmo";
		case EditorIconType.OrangeRound: return "sv_icon_dot5_pix16_gizmo";
		case EditorIconType.RedRound: return "sv_icon_dot6_pix16_gizmo";
		case EditorIconType.PinkRound: return "sv_icon_dot7_pix16_gizmo";
		case EditorIconType.GreyDiamond: return "sv_icon_dot8_pix16_gizmo";
		case EditorIconType.BlueDiamond: return "sv_icon_dot9_pix16_gizmo";
		case EditorIconType.CyanDiamond: return "sv_icon_dot10_pix16_gizmo";
		case EditorIconType.GreenDiamond: return "sv_icon_dot11_pix16_gizmo";
		case EditorIconType.YellowDiamond: return "sv_icon_dot12_pix16_gizmo";
		case EditorIconType.OrangeDiamond: return "sv_icon_dot13_pix16_gizmo";
		case EditorIconType.RedDiamond: return "sv_icon_dot14_pix16_gizmo";
		case EditorIconType.PinkDiamond: return "sv_icon_dot15_pix16_gizmo";
		default:
			throw new ArgumentOutOfRangeException("iconType", iconType, null);
	}
}