as far as I know there is no (regular scripting) identifier to check what alias called another.

best way to do this is to make a variable which holds the calling aliases name in it...

Code:
/alias1 {
  set -e %alias.name alias1
  ;do stuff
  alias3
}

/alias2 {
  set -e %alias.name alias2
  ;do stuff
  alias3
}

/alias3 {
  if (%alias.name == alias1) {
    echo -a Alias1
  }
  elseif (%alias.name == alias2) {
    echo -a Alias2
  }
  unset %alias.name
}


(the /set -e switch removes the var when mIRC exists and is v6.17+)

If it ain't broken, don't fix it!