Hi PPR,
The one thing that all VoPo's seem to share is a new postwar barrel. This barrel can be identified quite easily, as the crown (the thicker area on which the front sight rests) is not smooth like normal lugers, but is roughly cut. The barrels have postwar crown/N stamps as mijc mentioned.
The East-Germans did no effort to disguise the herecy of the parts, so you can find combinations of DWM/Simson/Erfurth/Krieghoff toggles, frames and small parts. These parts are force-matched to the frame, but original stamps are usually still present. I have a VoPo with pre-1918 frame and toggle (imperial eagle on front link), 1936 Mauser receiver and 'fresh' VoPo barrel.
The firing pin is usually the only part that has a roughly etched number.
There are also Lugers from Russian and Hungarian supplies, reworked by some large German gunstores. These are usually better quality than the VoPo's (no noticable service life) and usually have renewed barrels (of old VoPo stock, we're talking about post-1990 reworks) and some have russian capture marks (a stamped cross-mark). These are usually good quality full-dip deep black refinished guns, with aftermarket wooden grips and force-matched VoPo surplus magazines (extruded 02/1001). These guns usually are completely matched, although it's difficult to say if parts have been replaced. Usually small springs are renewed.
VoPo's originally have the bulls-eye brownish grips. The vertical-lined black grips are usually found on Russian/Hungarian pistols, as the Russians stored their captured lugers without grips (dipped in oil drums). When lugers were pressed into service, replacement black grips were added, resembling the grip patterns found on the Tokarev and the Frommer
