This rather small stewardess pinback is Pennsylvania Central Airlines (PCA The Capital Airlines).
Here’s the story on PCA. If the dates are correct on that page, it means that this pin dates to a time prior to 1948, when the company became Capital Airlines, dropping the “Pennsylvania” from its name.
I passed this by at first until the owner of the antique store (a building crammed so full of stuff that only narrow, one-person passageways led from one area to the next) pointed it out as airline related. Glad he did.