Cat regularly playing — a sign of affection (4)
I believe the answer is:
lynx
'cat' is the definition.
(I've seen this before)
'regularly playing a sign of affection' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'a sign of affection' becomes 'x' (used to represent a kiss).
The alternating letters of 'playing' are 'lyn'.
'lyn'+'x'='LYNX'
(Other definitions for lynx that I've seen before include "Wild cat noted for keen sight" , "Cat - northern constellation" , "Northern short-tailed wild cat(s)" , "Wild cat; sounds like chain" , "One of the wild cats" .)