Two places that merged, as you might expect. From an article on bygone Baltimore:

Ballow's at 2115 W. North Ave. gave the world what it now takes for granted, the formidable hot dog-and-bologna combination. In this creation, grease from the bologna mixes with the grease from the hot dog, and both find their way into the bread to form an unforgettable aroma, taste and aftertaste -- and 200 points on your cholesterol count.

Sounds . . . horrible, to be honest. I'm no prude when it comes to this sort of thing, but this doesn't sound appetizing.

It was probably fantrastically delicious. I'll never know.