Below is a list of the standard Wirt imprints. Along with some of my notes. If you have a Wirt pen with a different imprint, then I would very much like to hear from you.

PAUL E. WIRT PAT. FEB - '85
Above is the first standard Paul Wirt imprint. All of the fountain pens bearing this imprint would be over feeds, and these are not easy to find.

PAUL E. WIRT FOUNTAIN PEN
PAT'D JUNE 27, 1882 FEB 3, 1885
Though this imprint bears an earlier date than the imprint above, fountain pens with this imprint were made later. The 1882 date refers to Marvin C. Stone's fountain pen patent. In the late 1880's Paul Wirt was caught up in many law suits, protecting his fountin pen patents from infringements from the likes of F.C. Brown of the Caw's pen company. In all of these trials the defending parties raised the question of Stone's earlier pen patent that was very similar to Paul Wirt's. Around 1889 Wirt acquired the Stone patent rights and began imprinting that date on his pens. If you find an early Wirt overfeed fountain pen, chances are it has this imprint.

PAUL E. WIRT FOUNTAIN PEN
BLOOMSBURG PA USA
PAT'D APRIL 7, 1903
This imprint appears on Wirt's vented underfeed eyedropper fountain pens with a vented nib.

PAUL E. WIRT FOUNTAIN PEN
BLOOMSBURG PA
This imprint appears on the Wirt desk pens and celluloid fountain pens with a vented underfeed and a ventless nib.

WIRT FOUNTAIN PEN
BLOOMSBURG PA USA
PATENTED
This imprint appears on fountain pens with screw caps that have the vented underfeed

(No imprint)
Many Paul Wirt lever filler fountain pens have no imprint at all. You can identify them by a vented underfeed and the nib should have a "W" inside a wreath