I have suggested this as a Feature Request as it currently does not exist:
For a conversion that does not include subtitles (i.e. No subtitles are found in the original file)
allow a checkbox/option to append the tag -NoSubs to the output filename
However, is it possible there could be a workaround right now?
In Handbrake Preferences, there is the option "When Done" (checkbox) Send File To (Browse) Arguments:
Is it possible to create some kind of Batch file to run the Handbrake CLI to scan the encoded file for subtitles and if no subtitles are found, run a DOS command to append -NoSubs to the filename?