it's entirely clientside in client\data\luafiles514\lua files\signboardlist.lub
and thus can't be disabled server wise.
{
"prontera", // Map
159, // x coord
192, // y coord
10, // sign height
IT_SIGNBOARD, // type
"유저인터페이스\\item\\al_warp.bmp", // ressource path
" Warper", // Text shown
"#0x00FFFFFF" // Text color
},
You can simply empty that file.