Boyd’s Bible Dictionary:
(signal). A lighted signal for warning (Isa. 30:17).
Concise Bible Dictionary:
Signal pole placed on the top of a hill (Isa. 30:17). Israel should be so reduced in prosperity and in number as to become like a solitary “tree bereft of branches” (margin).
Strong’s Dictionary of Hebrew Words:
Meaning:
probably for 766; a pole (as a mast or flag-staff)