It’s possible that our box owner was a doctor or nurse. The letter “c” with a line over it is clinician’s shorthand for “with.”
It represents the Latin word cum, most commonly heard around graduation time, when people can graduate with praise, with great praise or with highest praise–cum laude, magna cum laude and summa cum laude, respectively. There’s a parallel shorthand mark made from its antonym, sine; the letter “s” with a line over it means without.
Other abbreviations cut from the same cloth include “a” with a line over it for ante (before), “p” with a line over it for post (after), and “q” with or without a line, for quaque (each, used in the context of telling someone how frequently to do something).
You could compare this recipe to the waffles divan recipe, which, starch aside, is also a broccoli, chicken, and canned soup preparation.
From a box sold in Chicago, Illinois.
Broccoli Hot Dish
In 3 Tbsp. butter cook until tender 1/2 c. celery. Cook one box Uncle Ben’s long grain rice according to directions. Cook 1 pkg. frozen chopped broccoli. Mix together with one can cream of chicken soup. 1 small can evaporated milk (not 13 oz.). Put over chicken in long pan. Top with 1 jar Cheez Whiz. Bake 1/2 hour — 325 deg.