OP wants to know how to display a player's name automatically on a sign.

You can have a look at the "Wiring" section of this amazing guide by hobukastan: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2127986941

The code you have to use is "{playername}" - as explained in the guide, each player will see their own name, there is no way to "read" the name of a specific player to be shown to other players.

Thanks a lot @entuland