Springfield Armory started using a stamped trigger guard in early 1945.  These had a sharp hook milled on the tab that locks into the trigger housing when you close it.  The later post war stamped guards lacked this milled hook. Both versions had the notches on the side.  When International and Harrington & Richardson started manufacturing trigger guards they didn't include this notch.  If you can determine that a notch or part of a notch shows on either side of the guard than it is a Springfield "second".  IHC and HRA made no attempt to do this proceedure.