Signior regularly holds arm up in the air (2,5)
I believe the answer is:
in limbo
'up in the air' is the definition.
(I've seen this before)
'signior regularly holds arm' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'holds' means one lot of letters goes inside another.
'arm' becomes 'limb' (I've seen this in another clue).
The alternate letters of 'signior' are 'ino'.
'ino' going around 'limb' is 'IN LIMBO'.
(Other definitions for in limbo that I've seen before include "pending" , "Up in the air" , "on the back burner" .)