There isn't what you're suggesting. I suggest though that you can either:

• use the robots.txt to block Google indexing the media
• if you're happy that any user can access all media then you can use standard web.forms authentication to make sure they're logged in
• create your own MVC Controller or Html Handler that takes media ID as an argument and returns the file without exposing the actual location.

Your surface controller might look like:

public MediaSurfaceController : SurfaceController
{
    public ActionResult Download(int id)
    {
          if (User.IsInRole("MyUserRole") == false)
              return HttpNotFound();

          var mediaItem = Umbraco.TypedContent(id);
          string fullName = Server.MapPath(mediaItem.Url);

          byte[] fileBytes = GetFile(fullName);
          return File(fileBytes, System.Net.Mime.MediaTypeNames.Application.Octet, fileName);
      }

      byte[] GetFile(string s)
      {
          System.IO.FileStream fs = System.IO.File.OpenRead(s);
          byte[] data = new byte[fs.Length];
          int br = fs.Read(data, 0, data.Length);
          if (br != fs.Length)
              throw new System.IO.IOException(s);
          return data;
      }
  }

There's also a (commercial) package that offers this:

https://our.umbraco.org/projects/website-utilities/media-protect/

Thank you gents, I shall investigate these!

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