[Admins]

The server doesn't send signs, it's also a way to reduce the data that is sent to the client. The detection for if someone is touching a sign is done on serverside, and the translated text is then sent to the client. On the clientside it is displaying the sign, and you can check with 'if (playerreading)' (or player.reading in new scripting engine) to know if the player is reading a sign.
Normally the lag is not that much that you actually notice a delay between touching and seeing the sign, for a fade-in effect it might be interesting to do your own sign-system. Eventually it should be made easier to fade-in / fade-out GUI controls.