Of course there’s no actual official ‘china export’ mark and that is just what some Chinese factories were claiming when they were caught slapping a (accidentally mis-spaced) CE conformance mark on their products! The EC made a statement on this back in 2008 [1] so everyone knows what game they are playing.
Notably, that link does not repeat that "some Chinese factories were claiming...". It just states that some people put it on noncompliant products. It is unclear whether any Chinese factories ever made that claim.
1. https://www.europarl.europa.eu/doceo/document/P-6-2007-5938-...