Chinese "Currency"

Correct.

Many communist countries issued "visitor money" or more formally a "foreign exchange certificate", only available to foreigners and only exchangeable into "normal" money of that country by individuals licensed to be handling them. Converting it back into foreign money again was also tightly controlled, if not outright forbidden.

The theory is to protect the purity of the revolution by preventing foreigners from being able to bribe locals with local money. In practice, it had much more to do with preventing the operating of a foreigner-driven black market and to create an artificially high exchange rate advantageous to the government issuing the notes, allowing them to extract as much hard currency from the tourists as possible.

North Korea was so paranoid at one stage that they had two different sets of "visitor money" made: one set for use by Western capitalist tourists, the other for use by tourists from fellow communist countries.

China no longer issues such notes. The only "visitor currency" still in use today is Cuba's convertible peso, and even this is being phased out.

I was there in 1991 and still have a few FEC's from that time