The story
Macy's and Gimbels (without the apostrophe) were popular department stores located within two blocks of one another in Midtown Manhattan in New York City; the latter store is now defunct.
Etymology from Wiktionary, CC BY-SA 4.0.
does Macy's tell Gimbel's
Today it means: A rhetorical question with the implied answer being that competitors do not share business secrets with one another. Full definition →