Yankee parking Sierra -- European knocked over notice (4)
I believe the answer is:
espy
'notice' is the definition.
(I've seen this before)
'yankee parking sierra european knocked over' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'parking' becomes 'p' (abbreviation on road signs).
'sierra' becomes 'S' (phonetic alphabet: alpha, bravo, charlie etc.).
'european' becomes 'E' (abbreviation e.g. EU).
'knocked over' says the letters should be written in reverse.
'y'+'p'+'s'+'e'='ypse'
'ypse' reversed gives 'ESPY'.
(Other definitions for espy that I've seen before include "Catch a glimpse of" , "Spot, notice" , "Observe, notice" , "Perceive" , "Spot; observe" .)