I always thought that the "SW" board on the approach to tunnels etc was for "Sound Whistle", but I read something the other day suggesting it was "Short Whistle". Can anyone on the list put me right? Ok it'll take more than that to put me right, but you know what I mean! JohnP MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.