Hi Rod,
All M1900 lugers had the "in the white" polished thumb safety area.
When the Germans went to the M1906 Navy and M1908 Army models, they switched to "Gesichert" stamping.
The Swiss decided to stay with the "in the white" feature through all M1900 variants, all M1906 variants, all M1906W+F Bern variants, but finally dropped it with the M1929 Bern luger production.
Regards,
Pete...