For example, my phone would automatically sign this post with my signature. If I programmed a bot, I could sign as myself or as a bot, but not as another registered human. So you'd know the post came from me or a bot I've authorized. Theft or fraud with digital signatures would be criminalized, it isn't already.
Your comment is wild, by the way. You think people should be allowed to run a bot farm, as long as they can digitally sign for it... but people who don't pay for a signature should be arrested?
I'm pretty sure it's already illegal to steal someone else's signature in some jurisdictions.
There would be no legal requirement to use a signature. No change there. Just as you cam send postal mail today with a return address and no name, and you can buy items with paper cash, and so forth. The government would give out verified signature, or the phone providers, and it'd be free. I don't really have the answers.