Sign initials on line, entering office (3)
I believe the answer is:
leo
'sign initials' is the definition.
'leo' can be an answer for 'sign' (star sign). I am unsure of the 'initials' bit.
'on line entering office' is the wordplay.
'on' says to put letters next to each other.
'line' becomes 'l' (used when specifying particular lines from a poem).
'entering office' becomes 'eo' (this could be a standard abbreviation which I don't know about).
'l' next to 'eo' is 'LEO'.
Can you help me to learn more?
(Other definitions for leo that I've seen before include "Horoscope sign" , "Fifth sign of the zodiac" , "Cancer, ___, Virgo" , "sign of summer" , "Pope" .)