Wrong event. on PING is to capture the PING? PONG! event (/help on PING). What you want is the on *:CTCPREPLY:PING *: event.

Code:
alias ping {
  if $show {
    echo -atic ctcp * Pinging $$1
  }
  .raw privmsg $$1 $+(:,$chr(1),PING $ticks,$chr(1))
}
on *:CTCPREPLY:PING *:{
  echo -atic ctcp * Ping response from $nick $+ : $round($calc(($ticks - $2) / 1000),2) seconds from $server
  .raw NOTICE $nick :Ping response from $nick $+ : $round($calc(($ticks - $2) / 1000),2) seconds from $server
  halt
}


cool