Sign first of reports in Spanish port (5)
I believe the answer is:
virgo
'sign' is the definition.
(Virgo is an example)
'first of reports in spanish port' is the wordplay.
'first of' suggests taking the first letters.
'in' indicates putting letters inside.
'spanish port' becomes 'vigo' (I've seen this before).
The initial letter of 'reports' is 'r'.
'r' placed inside 'vigo' is 'VIRGO'.
(Other definitions for virgo that I've seen before include "Zodiacal sign" , "Maiden" , "A constellation, a cluster" , "Large constellation between Leo and Libra" , "number of stars" .)