Purchase Request Auto Signature, how to stop this?

Scenario:

User JOHN creates a new purchase request PR, on the signature user assignment he is the first to sign PR. After creating the PR, the PR is automatically signed.

I suppose this comes from the actions in the workflow that fires when the PR is created or updated, when we want to stop this what is the proper configuration of:

  • workflow rule;
  • user assingment;
  • user assignment rules;

Thanks in advance!