At Beijing's largest antiques market, Panjiayuan, among the Mao statues, posters and secondhand books are prominent signs warning against the sale of publications that might have state secrets or "reactionary propaganda."
Some of the signs display a hotline number so that citizens can tip off authorities if they witness an illegal sale.
China's antiques and flea markets were once a gold mine of documents for historians, but now the signs are emblematic of the chill that has descended on their ability to do research in the country.
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