It's simply part of a roll die system, it was called a 'foot'.
On hand operated roll die operations where the die was imprinting lines of small lettering or numbers, a 'foot' was generally added at the front and end of the line. This let the die land on the metal and escape it at the end of the roll with a 'foot'.
That avoided the common problem of a very deep initial & final imprint if the die is made w/o these.
A foot can also be found in a longer blank space between lettering to avoid the same problem. It just supports the die traveling accross the open space so it maintains it's level and again avoids an overly deep initial impression when it starts imprinting the lettering again.
The foot can be anything,,a bar, star, star burst design, cross, anything the die designer decides.
Winchester bbl lettering from the hand op roll die machine era usually had a simple heavy line/bar preceding and after the lettering lines.
Don't read too much if anything into them as far as a hidden meaning.
These are all obsolete by modern standards of computer controlled roll die impressions. Impression depth and placement is strictly controlled throughout by machine now and the hand operation is limited to perhaps placing and removing the part from the jig in between operations. Even the latter may be robotic now.
But the 'foot' may still be incorporated in a roll die for decorative purposes anyway. Many former die imprint operations are going to laser marking and other quicker and less expensive methods.