Thank you for your post.
At this time, there is no script step to activate the Signature option in a Container field. This must be done manually.
I recommend that you enter this suggestion into our Feature Requests web form at:
The entries into this web form populate a database file hosted by Development and Product Marketing, where they are discussed and considered for future releases. Although I can easily copy your post and paste it into the web form, there are a couple of questions asked that only you can answer.