Already made a while ago by wrewolf, nobody knows him but he was a great developer. Here's the plugin: https://github.com/wrewolf/Minecraft-MP-plugins/blob/master/PortalW.php
First line "w:" (without quotes) Second line the level name Third line "tp" (without quotes) But this plugin tis made to tp you to the spawn in another world
You know that I was going to put a sign portal thing in SAO-MCPE right? Or did I not tell you guys lol