Error "undefined reference" to my signals [on hold]

I am getting undefined reference to 'Initializer::draw()' for this code:

I don't know what to do with it. I know that there is no need to implement a signal in cpp. So why is that happening?

header:

class Initializer : public QThread
{
    Q_OBJECT

public:
    Game* game;
    explicit Initializer(QObject* parent = 0);

signals:
    void draw();

protected:
    void run(void);
};

cpp:

void Initializer::run(void)
{
    game->Initialize();
    emit draw();
}
Initializer::Initializer(QObject *parent)
    : QThread(parent)
{
}

Can anyone help?