Todd, as others have stated, that raised lettering is simply a mill mark.
Such mill marks were typically seen on hot-rolled structural members (such as the angles used as frame members for the model "H").
Today, very few mills, either domestic or foreign, use those mill marks. Instead, structural members are now affixed with adhesive labels indicating the mill, the heat number, member size, etc.
Not only do the labels contain more information than the old mill marks, but they probably save the mill some $$ as the rolls don't require the inscribed lettering that leaves the raised lettering on the product.