Unconcealed weapons are a sign of welcome! (4,4)
I believe the answer is:
open arms
'a sign of welcome' is the definition.
(I've seen this in another clue)
'unconcealed weapons' is the wordplay.
'unconcealed' becomes 'open' (associated in meaning).
'weapons' becomes 'arms' ('arm' can be a synonym of 'weapon').
'open'+'arms'='OPEN ARMS'
'are' is the link.
(Other definitions for open arms that I've seen before include "With which one is heartily welcomed" , "Welcomers" , "welcome wiyh....,....greet warmly" , "Welcoming attitude" , "Welcome with . . . . . . . . , a warm uninhibited greeting" .)