Neue Photographische Gesellschaft

The "NPG" logo changed a bit during the years in its boundary but the actual letters NPG remained looking the much the same. They are shown in this catalogue of early NPG cards. As explained there, NPG reused the early numbers in the 1920s, and the particular logo used on our example cards 2181 and 871 (see next page) was not used before number 1500 of the original series, which can be used to distinguish earlier cards. Other logos used were a star and crescent and a flag with a star on it, see the next page.

The Neue Photographische Gesellschaft (NPG) was the first and biggest early producer of real photograph postcards. Arthur Schwarz (1862-1944) founded the company in 1894 in Berlin-Schöneberg, and there were later subsidiary companies in other countries. The company closed in 1921, although the NPG trademark and the postcard department were acquired by E. A. Schwerdtfeger and ran until WW2.
In 1908 NPG left the P.R.A. after which 1909 is the registration date in the logo.

NPG having been so big, there is plenty of information about it on the web. Here is a (German language) site dedicated to NPG. Here is a good account in English (TPA).

NPG advert 1908