Ah, I thought you wanted to track both set and unset of these modes. Try:
Code:
on *:mode:#: {
  if ($me ison $_botchan) && ($regsubex($gettok($1,$iif((- isin $1),2,1),43),/[^iRmN]/g,$null)) {
    msg $_botchan $chan Modes: + $+ $v1 set by $nick
  }
}
This code assumes that if both +<mode(s)> and -<mode(s)> are set in the same mode string, the "-" modes will preceed the "+" modes, which afaik will always be true.