How to add sign on Sales Invoice?And which format?

Good day, recruitment-nirm.

I'll share a few details on how to come up with signatures in QuickBooks Online (QBO).

Currently, adding a signature  to an invoice isn't available in QuickBooks Online. As a workaround, you can insert the signature through the Attachments section. On the invoice creation screen, simply click on the Attachments box, then add your signature image from there. 

Meanwhile, you can look and integrate a third-party app that will allow you to add your signature. Here's how:

1. Go to the Apps menu at the left pane.
2. Select the Find Apps tab, and then type a keyword in the search bar.
3. Click the magnifying glass to search, and then choose the app that suits your need.

Need help creating invoices for your customers after creating a template? You can check this article for the steps: Create invoices in QuickBooks Online. 

If there are other things that you need to show on your invoices, please let me know. I'm always here to help. Have a good one.