Sign up mountain seen by eccentric figure (7)
I believe the answer is:
placard
'sign' is the definition.
(I know that placard is a type of sign)
'up mountain seen by eccentric figure' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'mountain' becomes 'alp' (the Alps are a mountain range).
'seen by' says to put letters next to each other.
'eccentric figure' becomes 'card' (card can mean an eccentric person).
'alp' written backwards gives 'pla'.
'pla'+'card'='PLACARD'
(Other definitions for placard that I've seen before include "Printed notice" , "Notice carried for public display" , "Slogan or message of protest on board" , "Bill" , "what may be carried in a demo" .)