Herb,
The Grenzpolizei were formed in the 1919 to early 20s period to patrol the Eastern Frontier along the Polish and Czech borders.
On page 118 ~Uniforms,Organization & history of the German Police~ by Angolia and Taylor.
"Frontier Protection/Frontier Police/Frontier Protection Police (Grenzschutz/Grenzpolizei/Grenzschutzpolizei). Frontier police existed in border states during the Weimar period, as a federal border control service."
A photo of my Grenzpolizei unit marked (G.P.349) 1914 Mauser. Magazine is faintly marked G.P. 1.
Photo of a Grenzpolizei Officer dated 1919.
Ron