My guess is never. The universal train icon for signs has a funnel and a cow-catcher, and it's a long time since a train looked anything like that. Same goes

My guess is never. The universal train icon for signs has a funnel and a cow-catcher, and it's a long time since a train looked anything like that. Same goes for the universal sign for telephone - nothing like a modern cordless handset. We can already seen this in action as the icon for 'mp3' on signs looks like a first-gen ipod. Already no players (even ipods) look like that, but I think it will stick around for a long time. Some things get stuck as icons and the original meaning is lost with the sands of time. Once the icon is assigned to a meaning for most people, it sticks. There's no reason to update the icon, even if it no longer represents the object, because everyone agrees on the meaning.