It is not a factory application. If I was to guess, I would say at some point it was a tab or similar to keep the glove box door from opening. Here is a factory shot from 1954, there is nothing there to warrant that screw.
http://www.flickr.com/photos/advance-design_parts_co/8256653524/in/set-72157632199330381
Very original 54' dash, again nothing there.
http://www.flickr.com/photos/advance-design_parts_co/8130525955/in/set-72157631870734114
One more.
http://www.flickr.com/photos/advance-design_parts_co/8130519563/in/set-72157631870734114