SetSignLines does not work

[nixi]

Hi,
I have started using lua yesterday and I just can not get past this problem. I need to update all lines of a specific sign. "World:SetSignLines()" Either does nothing (if called in a function started by a hook) or it throws out an error (if started in an independent function). How can I use this properly?

function poiMain(Split, Player)
  World:SetSignLines(58, 64, 42, "test", "test", "test", "test")
  return true
end

Code:

[15:34:37] LUA: Plugins/PointsOfInterest/functions.lua:52: attempt to index global 'World' (a nil value)
[15:34:37] Stack trace:
[15:34:37]   Plugins/PointsOfInterest/functions.lua(52): (no name)
[15:34:37] Stack trace end
[15:34:37] Error in plugin PointsOfInterest calling function <callback>()