How to add site collection wide global status?

Hi developers,

I have the requirement to add a global Status bar to all sites of a site collection without deploying anything.

I tried to add the following Java script code to the master page (with SharePoint designer), but it does not work.

<div id="MSO_ContentDiv" runat="server">
 <a name="mainContent"></a>
 <asp:ContentPlaceHolder id="PlaceHolderMain" runat="server">
 </asp:ContentPlaceHolder>
 <script type="text/javascript">
  AddStatus('We are currently working on the site. It is read only.', 'red');
 </script>
</div>

Any ideas how to add a globally visable status bar to the whole site collection?

Best regards,

Björn