Determine display mode of sharepoint page

In case you are using a team site :

    if (Microsoft.SharePoint.SPContext.Current.FormContext.FormMode == SPControlMode.Edit)
    {
        ltr.Text = "EditMode2";
    }
    else
    {
        ltr.Text = "ViewMode";
    }

in case you are using a publishing site:

if (Microsoft.SharePoint.SPContext.Current.FormContext.FormMode == SPControlMode.Display)
  {
   // your code to support display mode
  }
  else // Microsoft.SharePoint.SPContext.Current.FormContext.FormMode = SPControlMode.Edit
  {
   // your code to support edit mode
  }