It is compulsory for labeling to be affixed to all sunglasses when being sold. So, if there is no label affixed with the following standard number for your country or all the standard numbers plus the CATEGORY or CAT. # on it just dont buy them.
The three main world sunglasses standards are:
AUS/NZ - AS/NZS 1067:2003
EU - EN ISO 12312-1:2013+A1:2015
USA- ANSI Z80.3:2015