Jerry,

"Anton Sodia" was active from 1870 till after WW2. I would attempt reading the numbers like this:
15.3 = bore size in mm (or choke?)
3183 = serial number
1495 = proof house number ("Beschussprotokolnummer")
20 = year of (definite) proof - 1920
5139.19.15.0. could mean an earlier barrel proof:
5193 = proof house number
19 = year of proof - 1919
15.0 = bore size (in the rough, before finishing?), or maye choke size-?

- Jani