Ansco professional sheet films have the following notches to permit easy identification in the darkroom The emulsion side of the film is toward you when the notches are in top edge of the upper right hand corner (or in the bottom edge of the lower left-hand corner).

This notching system applies to 3 1/4 x 4 1/4 and larger sizes of Ansco films. All sizes of Ansco sheet films smaller than 3 1/4 x 4 1/4 are marked with a single, shallow notch in the usual position. This small notch is used only for identification of the emulsion side and is not for indication of the emulsion type.


From Ansco Formulas for Black and White Film by GAF, 1948 – Provided for historical reference.