Bob, you can pretty much tell cause the black paint is either black or not, there are no shades of gray. Do a search for a Heller with the anchor trademark or a Malsh & Ambronn, those are 2 guys I know painted their motto's. When the paint comes off it often peels and most often where the runners have rubbed.
One sure test is to use acetone. If the motto comes off you will know it was paint!! :>
-I'm kidding!!
IMHO the Wingen you show is burnished.
Lastly the more time I spend in this hobby the less I do to these things.
If ever there is ANY doubt do nothing!!