I found a comment in one of my environment files reminding me how to prevent commands prefixed with a space from being logged in BASH's history file:

export HISTIGNORE="&:[ ]*:exit"

Fortunately the comment pointed me back to the original source of the trick:

The Definitive Guide to Bash Command Line History - good coders code, great reuse

Let me teach you how to work efficiently with command line history in bash.