Delete signature file, and delete files that fail signature validation.

I wasn't quite sure on the wording for the new command line flag, so let me know your thoughts. For #335 (closed) & #336 (closed)

Approver's checklist:

• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent with existing code
• This feature/change has adequate documentation added (if appropriate)
• No obvious mistakes / misspelling in the code