Resistbot is on it. It only takes 2 minutes to add your name.
Text USPS to 50409
You will be asked a couple of questions and then your name will be added to the list of over 1 Million Americans who have already signed. I'm not on Twitter but apparently there's a long list going (you can opt out of having your name appear) that's driving even more signatures.
You can also DM USPS to @resistbot on Twitter or Messenger.