Legal authorities excluding one sign (8)
I believe the answer is:
notaries
'legal authorities' is the definition.
(notaries are legal officials)
'excluding one sign' is the wordplay.
'excluding' becomes 'not' (not including).
'one sign' becomes 'Aries' (star sign).
'not'+'aries'='NOTARIES'
(Other definitions for notaries that I've seen before include "legal professionals?" , "Legal workers" , "Legal agents - senorita (anag)" , "Senorita in search of officials authorised to witness documents" , "They witness official documents" .)