[SARG]

This is what I've found on the net so far on the model 4.

Second Variant (World War I production.)

Left side of slide marked (in capitals) “SELBSTLADE-PISTOLE CAL. 7,65. WALTHER’S-PATENT” on one line above the Walther banner.
Right side of slide marked (in capitals) “CARL WALTHER WAFFENFABRIK ZELLA ST.BLASII” on one line, or in rare cases blank.
6 vertical slide serrations.
Adjustable raised rear sight in a dovetail mount.
Most front sights were hemispherical, but a few were triangular.