|Wikipedia has more information about bomb (symbol).|
The bomb icon is a symbol designed by Susan Kare that was displayed inside the System Error alert box when the "classic" Macintosh operating system (pre-Mac OS X) had a crash in which the system decided it was unrecoverable.
The bomb symbol first appeared on the original Macintosh in 1984. Often, a reason for the crash including the error code was displayed in the dialog. If a person was lucky, a "Resume" button would be an option, which could be used to dismiss the dialog and force the offending program to quit, but most often the resume button would be grayed out and the computer would have to be restarted. Originally, the resume button was unavailable unless the running program had provided the OS with code to allow recovery by passing a resume procedure to InitDialogs. With the advent of System 7, if the OS thought it could handle recovery, a normal error dialog box was displayed, and the application was forced to quit. That was helped by the classic Mac OS providing a little bit of protection against heap corruption using heap zones, if the application was to crash and the application's heap was corrupt, it could be thrown away.
The debugger program MacsBug was sometimes used even by end users to provide basic (though not always reliable) error recovery, and could be used for troubleshooting purposes. Mac OS Classic bomb boxes were often ridiculed for providing little or no useful information about the error; this was a conscious decision by the Macintosh team to eliminate any information that the end user could not make sense of.