Just start a comment with "Approved" (or a custom regular expression) to sign-off without ever leaving GitHub. PullApprove can be configured by a .pullapprove.yml YAML file in the root of your repo. With it, decide exactly what "approval" means to your team.
PullApprove is a tool in the Tools for GitHub category of a tech stack.
Here’s a list of reasons why companies and developers use PullApprove.