Try this one:
addEventHandler ( "onPlayerJoin", root,
function ( )
local name = getPlayerName ( source )
if name:find ( "#%x%x%x%x%x%x" ) then
setPlayerName ( source, name:gsub ( "#%x%x%x%x%x%x", "" ) )
end
end
)
addEventHandler ( "onPlayerChangeNick", root,
function ( _, new )
if new:find ( "#%x%x%x%x%x%x" ) then
cancelEvent ( )
end
end
)
P.S: Is a server side script.