This is a postcard sent from Beijing, China to Europe on March 22, 1917. When the postcard passed through Petrograd, Russia, the text written on the postcard was scratched off by an inspector, and the postcard was confiscated. A purple triangular check stamp is also stamped on the film, and no record of this check stamp can be found in the relevant Russian censorship documents.
Dear philatelist friends, can you tell me where in Russia this triangular inspection stamp was stamped? Is it in Petrograd?