National flags (7)
'national flags' is the definition.
('ensign' can be a synonym of 'national flag')
This is all the clue.
(Other definitions for ensigns that I've seen before include "standards" , "Sensing (anag)" , "US naval officers" , "Flags for naval officers" , "(Military) flags" .)
(Other definitions for standards that I've seen before include "Reference points for comparison" , "Flags for bases of measurement" , "Desired levels of quality" , "Principles of decent behaviour" , "Norms in flags?" .)