I was unaware of the existence of "sewing machine" perforations so I wasted some of the state's time and did a little research. I've learned something and been productive already today!
"Pin perforations are also uncommon. They are found on some state revenues and on some foreign stamps. They look like a string of little pin pricks, which is what they are. Pin perforations are uncommon because they don't do a great job of making the stamps easier to separate." (From
www.junior-philatelists.com)Here is a cover with a sewing machine perforated offered by Robert A. Siegel:
Sorry, the picture won't show even though it's uploading normally. It was a beautiful piece!



5c Green, Stone 2, Shuqualak Miss. Sewing Machine Perf (1 var). Mostly ample to large margins showing complete row of pin-perfs along right side, gum stains, tied by "Shuqualak Miss." circular datestamp on yellow cover to Gainesville Ala., multicolored 7-Star Confederate Flag and "SC" Patriotic Label die-cut and affixed at left, Very Fine, extremely rare sewing-machine private perf, with 1988 C.S.A. certificate stating stamp and perfs are genuine but declining opinion on use of label, Scott Retail $1,750.00