Sign of disapproval with uniform's short skirt (4)
I believe the answer is:
tutu
'short skirt' is the definition.
(I've seen this before)
'sign of disapproval with uniform's' is the wordplay.
'sign of disapproval' becomes 'tut' (a tut is a disapproving sound).
'with' says to put letters next to each other.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'tut'+'u'='TUTU'
(Other definitions for tutu that I've seen before include "Giselle's skirt" , "In which dancer may appear" , "Ballerina's costume" , "A ballerina's short skirt" , "South African archbishop, b. 1931" .)