To add a signature in Google Docs, you can create one by drawing a scribble and saving it, or use an existing image of your signature. To edit a signature, select the portion you want to change, resize or move it as needed, and save again. You can also automate tasks such as sending out signed documents by using templates with Zapier to autopopulate data from other apps like Google Sheets. With these features, you can easily create professional-looking signed documents without needing a dedicated eSignature app.