This is a simple script which displays your ping (in milliseconds) to the server via a custom window.
After loading the script and connecting to a server, the script will set a timer to ping all connected servers every 60 seconds. This will be displayed in the custom window list.

on *:CONNECT:{
  if (!$timer(pingservers)) { timerpingservers 0 60 scon -at1 pingservers }
  if (!$window($+(@,$cid,.Ping:*),1)) { window -nk0 @ $+ $cid $+ .Ping: - }
}

alias pingservers {
  if ($($+(%,pingResp,$cid),2)) {
    renwin $window($+(@,$cid,.Ping:*),1) @ $+ $cid $+ .Ping: >60000
    echo -t $window($+(@,$cid,.Ping:*),1) >60000
  }
  set %pingResp $+ $cid 1
  .raw PING : $+ $ticks
}

on ^*:PONG:{
  var %ticks = $ticks
  if ($($+(%,pingResp,$cid),2)) {
    var %ping = $calc(%ticks - $($+($,$0),2))
    if (!$window($+(@,$cid,.Ping:*),1)) { window -nk0 @ $+ $cid $+ .Ping:  $+ %ping }
    else { renwin $window($+(@,$cid,.Ping:*),1) @ $+ $cid $+ .Ping:  $+ %ping }
    echo -t $window($+(@,$cid,.Ping:*),1) %ping
    unset %pingResp $+ $cid
    haltdef
  }
}