How to Create a Sign Portal That Teleports You to Another World
Placing and Formatting the Sign
To make a working sign portal, place a sign on any solid block where you want the entrance to be. Right-click the sign to edit it, then type the destination on the lines. The exact syntax depends on your server's Multiverse setup, but a typical destination looks like a world name on the first line, optionally followed by coordinates on the next lines. For example, put the target world name on line one, then the X, Y, and Z values on the following lines if you want an exact landing spot. If you only want to send players to a world's default spawn, the world name alone is usually enough.
Confirming It Works
Once you save the sign, look at the text color. Green text means the destination was recognized and the sign is active. Red text means something is wrong — usually a misspelled world name, a world that doesn't exist in Multiverse, or a missing permission. Fix the text by right-clicking again and correcting the line. When the text is green, any player with permission can right-click the sign and be teleported. Test it yourself first before telling others about it, and stand clear of the sign so you don't accidentally trigger it while editing.