$signal = ($? >> 8) & 127;

00000000 00000000 CSSSSSSS EEEEEEEE

   >> 8

00000000 00000000 00000000 CSSSSSSS

   & 127

00000000 00000000 00000000 01111111 = 127
00000000 00000000 00000000 0SSSSSSS