I respond to 'Unsuccessful search terms' I observe in my web site admin page by filling in what I can throughout the site.
This week, 'perforation meaning' was one such term, so this is a post to address just what those little punched markings in your vintage pattern can mean.
The first individually packaged sewing patterns marketed for the home sewer came in the form of un-printed, pre-cut tissue pieces. Each piece was factory punched with perforations indicating the pattern piece letter or number (a few pattern makers, such as Vogue punched the entire name of the piece into the tissue). A schematic and legend was printed on the envelope or enclosed instruction sheet to correspond. Seam lines, darts or placement lines were also marked by perforations and a printed key accompanied the pattern by which the home sewer could determine what to do with these markings when constructing the garment. Even later pattern which were printed may also include some perforations.
Below, I have listed characteristics of markings as they were applied similarly by many different makers through the late 1950's. As different companies likely also had different markings, I indicated by maker to dispel some of the more unique markings.
Two to three large circles spaced apart or a series of two to three smaller circles placed closer together down the middle of the piece = Straight of Grain.
Two large circles close together or three larger circles arranged in a 'pyramid' formation at the straight edge of a piece = Place edge on center front or center back:
Large single circles spaced apart down the length of a bodice front, bodice back, skirt front or skirt back, etc. = Center Front or Center Back.
Small single circles along each edge of the piece = seam allowance given.
Two small circles spaced a short distance apart, toward top of skirt/trousers or bottom of waist = Natural Waistline.
Small circles in a series creating a triangle or wedged oval (whether vertical, horizontal or diagonal) = dart placement:
Two smaller circles spaced in a line, far apart across a piece = where to shorten or lengthen the pattern.
Large diamonds spaced in a line, far apart across a piece (mostly mail order patterns) = where to shorten or lengthen the pattern.
Two small circles spaced closer together = buttonhole placement & buttonhole length. When at the top of a sleeve cap, they are meant where the sleeve cap is to be aligned with shoulder seam of bodice.
A series of one to three small circles opposite a series of same number of large circles = pleats.
Two small circles placed close together vertically = match point or stop stitching point.
Large single circle = Button placement or stop stitching point.
Small single circle at a corner = clip to the circle from seam allowance.
Square markings (mostly Vogue) = buttonhole placement or match point.
Triangle markings (mostly Vogue) = match points between two pattern pieces, i.e. top of godet piece to insert of skirt front or back.
Series of small or large circles across a bodice front or back (mostly Butterick) = Line to cut a different neckline option:
Series of large or small circles along a neckline = Where to cut a neck facing from the piece.
Series of large or small circles down the length of a bodice or skirt piece = Where to cut a facing from the piece or where to cut the lining from the piece (be sure to add seam allowance, if applicable).
Two crosses spaced apart (mostly McCall) = line of gathering.
Two sets of small circles placed close together vertically with a distance between each set = line of gathering.
Square in line with a notch, some distance between will be specified in instructions (mostly Vogue) = line of gathering.
Series of small or large circles across a skirt, trousers, etc. = Cut a shorter length.
Series of small or large circles along the bottom of a skirt, trousers, etc. = hem line.
Large single circle at top of sleeve cap = match point to shoulder seam of garment.
Large set of circles along shoulder and underarm (side seam) edges (mostly Butterick, post 1939 Simplicity = Let-out given.
Two small circles spaced a short distance on sleeve = elbow location, in McCall patterns usually indicated by the horizontal darts printed on the pattern:
Series of small or large circles across a sleeve (mostly Butterick) = Line to cut a shorter length sleeve or placement line to add flounce, trim or embellishment. At the bottom of the sleeve, this can also mean where to cut a facing from the pattern piece.
Series of small or large circles along the bottom of a sleeve = hem line.
A very brief reference can be had via Threads Magazine re: the article I wrote for them in issue #132 on Working with Vintage Patterns.