It’s ‘visa’ not ‘VISA’. Why do so many people think it’s an acronym? It’s just a normal word.
See also: Most of the Windows people in my company's IT department write "MAC" instead of "Mac." Few of them work with networking, so I don't think it's related to MAC addresses.
Wikipedia seems to concur that this is common:
"Mac or MAC most commonly refers to... Macintosh, a brand of computers and operating systems made by Apple Inc."