Delete question mark in QML Dialog titlebar

[Locate]

I am using Qt 5.7. In my QML project I have several dialogs. In the titlebar of this dialogs there is a question mark under Windows. Under Mac there is no question mark. Is there a possibility to remove this question marks? Or alternatively is there a Signal to connect a Slot when the question mark is clicked?
My Dialog is something like this:

Dialog {
    property string appVersion: ""
    property color buttonColor: "#000000"
    property string branding: ""

    id: dlgAppInfo
    visible: true;
    modality: Qt.ApplicationModal
    width: 520
    height: 300

    signal signalClose()
    signal signalUpdate(bool silent)

    onVisibleChanged: {
        signalClose()
    }

    contentItem: Rectangle {
        x: 20
        y: 20

//My components
}
}

Edit: Added code tags -- @Wieland

[A Former User]

Hi! Not sure what question mark you're speaking of. Maybe it goes away when you set the title property of the Dialog?

[Locate]

Here is a screenshot of such a Dialog. I have marked the question mark. The title property is set.

[A Former User]

@Locate The image upload feature on our forum is broken (the image might be visible to you but not to anyone else). Please use an image hoster (e.g. https://postimage.io) and embed the file here with ![alternate text](url).

[Locate]

Here is a link for the Image https://s3.postimg.org/dkjhdm0ab/Unbenannt.png

[A Former User]

I don't think one can customize that for a Dialog. What you could do is to use a Window QML Type as the foundation for your own dialog item. You can customize almost everything with Window. You can change the buttons in the title by modifying the flags property. A list with all window flags can be found here: flags Qt::WindowFlags. And there's also the Window Flags Example.