Rosszul használod a CreateDynamic3DTextLabel függvényt. A helyes használata:
native Text3D:CreateDynamic3DTextLabel(const text[], color, Float:x, Float:y, Float:z, Float:drawdistance, attachedplayer = INVALID_PLAYER_ID, attachedvehicle = INVALID_VEHICLE_ID, testlos = 0, worldid = -1, interiorid = -1, playerid = -1, Float:streamdistance = 100.0);
A te esetedben:
MySigns[playerid] = CreateDynamic3DTextLabel(\"Loading...\", -1, 0.0, 0.0, 0.0, 70, playerid);