A police sergeant drew his gun during a stand-off with a knife-wielding robber and recovered a Hermes Birkin bag worth about HK$390,000 stolen from a businesswoman on the streets of Hong Kong, a senior officer said on Tuesday. But two of the robber’s accomplices escaped and remain at large.According to initial investigation, the woman posted the item for sale on the Carousell online selling platform last year, claiming the black crocodile-skin luxury bag was 99 per cent new and worth HK$399,000…