Amusingly, I have a "B.A. in CS". Given the subject, most people assume a B.S. if you just say "bachelors'", but in my particular case, they'd be wrong ;) I imagine this is somewhat like how you can get a doctorate in nursing.

(just wrapping up my own three magical letters too!)

I've seen this in many job descriptions, but in 30+ working years I've never seen an employer actually verify that a candidate had the credentials he claimed to have.

In my (admittedly anecdotal) experience, this requirement is often flexible. I tend to read it as "B.S. in CS, or sufficiently impressive relevant experience."