The terms appear in several forms that I suspect refer to the same material: "printed" or "stamped" jacket "patterns" or "shapes." The first occurrence is in this advertisement for a vendue sale managed by Philadelphian William Adcock. Among the many textiles he advertised, Adcock included "printed jacket patterns." The same term also popped up several times Philadelphia papers in 1777 and 1778.
The Pennsylvania Evening Post, September 7, 1776.
A similar term appeared in a New Jersey newspaper in 1778. Along with a variety of notions like stockings, gloves, and ribbons, William Chew stocked "men's stamped jacket shapes."
The New-Jersey Gazette, January 28, 1778.
In 1782, Isaac Smith of Hopewell township, New Jersey, was robbed by a group of armed men. They took a variety of textiles, silver, and guns. Among the yardgoods were "2 stamped jacket patterns of yellow jean" and "2 stamped handkerchiefs."
Detail of advertisement. The New-Jersey Gazette, April 24, 1782.
I suspect they are different ways of describing material intended for men's waistcoats, sometimes called jackets, especially when they included sleeves. Waistcoating was a popular material in the eighteenth century, but, in my experience, examples of this sort of material featuring patterns of color were woven, not printed; newspaper advertisements for "printed waistcoating" first appeared in 1807 and "printed vesting" in 1806, according to the "America's Historical Newspapers" database. The idea that "stamped" means printed and "patterns" and "shapes" refer to printed patterns (colorful patterns, not sewing patterns) is supported by the robbery advertisement, where "stamped jacket patterns" appeared alongside "stamped handkerchiefs," almost certainly printed kerchiefs like this one.
I look forward to eventually uncovering more evidence about these curious terms, but for now I've been unable to locate any other references or explanations. Keep your eyes open for me!
Update: Hillary Rizen brought this interesting waistcoat to my attention as a potential, albeit later, example of the sort of printed waistcoat to which these advertisements may refer.
Printed waistcoat, 1790s, from Christie's.
Update: Joseph Privott pointed me to several reference to "patterns" in Abbott Lowell Cummings's Rural Household Inventories (Boston: The Society of the Preservation of New England Antiquities, 1964). The 1768 estate inventory of Ebenezer Pierpoint of Roxbury, Massachusetts included "Superfine Cloth a pattern for a Coat" and "two knit patterns for Jacketts," (221). A "Nett pattern for Jacktt." appeared in the 1769 inventory of Captain Ebenezer Newell, also of Roxbury (226). I don't think these terms refer to the same thing as the above "printed jacket patterns," but instead to the yardgoods (cloth or knit/"Nett") required to make a certain garment. I've seen references to knit breeches "patterns" elsewhere before, but never to knit jackets. Intriguing.