In bash you can type:
ls `: whatever`
It's just a command substitution that produces an empty expansion. It gets abused as a comment because it usually has no effect on the program, but that isn't guaranteed. Consider
ls `: Don't use a $() here`
It also still requires a subshell to be created in order to run the command, so it slows your script down (however little that may be, but lots of them can add up).
Don't use this: use a proper