[mometsi]

The stores really were called Penneys (no idiot apostrophe present) until being gradually rebranded in the 70s and 80s.

some examples:

80s: https://commons.wikimedia.org/wiki/File:Downtown_Seattle_Pen...

70s: https://commons.wikimedia.org/wiki/File:FW_Woolworth,_Penney...

60s: https://commons.wikimedia.org/wiki/File:Penneys,_Eastland_Ma...

50s: https://commons.wikimedia.org/wiki/File:StateLibQld_1_46896_...

40s: https://commons.wikimedia.org/wiki/File:Seattle_-_Second_Ave...

[xp84]

Penney's was founded by James Cash Penney. The store was his store, that is, it was Penney's store. I think the omission of the apostrophe was kind of artistic license, but I'm only addressing the silliness of adding the "S," with or without an apostrophe, to something that isn't a person's name.