Policemen with special signs of approval for standards (10)
I believe the answer is:
yardsticks
'for standards' is the definition.
(yardstick is a kind of standard)
'policemen with special signs of approval' is the wordplay.
'policemen' becomes 'yard' (Scotland Yard is the Metropolitan Police HQ).
'with' says to put letters next to each other.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'signs of approval' becomes 'ticks' (I've seen this before).
'yard'+'s'+'ticks'='YARDSTICKS'
(Other definitions for yardsticks that I've seen before include "Benchmarks" , "Standards" .)