If we want the shell to ignore certain signals, then we can call the trap command followed by a pair of empty quotes as a command. Those signals will be ignored by the shell process shown by either of the following commands:
$ trap " " 2 3 20 $ trap " " INT QUIT TSTP
The signals 2 (SIGINT), 3 (SIGQUIT), and 20 (SIGTSTP) will be ignored by the shell process.