Hello, AY2029.

Susan's reply is almost a year old. They might not be able to get back to this thread. However, I'm more than happy to show you how to insert a signature. 

One way to do this is to 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. 

Another way to do this is to use an imported custom form style. You would create a template through MS Word, then you can insert images including your signature from there. Before doing this, make sure the Import style feature is turned on:

1. Click the Gear icon, then choose QuickBooks labs. 
2. Scroll down, then toggle the Import Style feature to on.
3. Click Done. 

I highly recommend reading this article for a guide on how to do this: Import custom form styles for invoices or estimates. 

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

You can also read other articles from our Help Articles page. Feel free to browse a topic then look for an article of your choice. 

I'd be more than glad to offer assistance again if you have troubles accomplishing your tasks in QuickBooks Online.