Cab signal (4)
I believe the answer is:
hail
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cab signal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for hail that I've seen before include "Precipitation - old greeting" , "Call from a distance" , "Greeting - falling stones" , "a drop of the hard stuff?" , "Greet enthusiastically" .)