I want to add a signature to the sales receipt ( we use as an official tax receipt and a signature is required

Hi 4kgray-sasktel-n,

Welcome to Community!  I can see the importance of having the ability to apply signatures to your sales receipts.  However, this currently isn't available in QuickBooks Online.  I recommend reviewing third party apps, for the best fit for your business needs.  If you would like to see this feature available in future updates, please don't hesitate to submit a suggestion to our Development Team by going to Settings ⚙ and select Feedback. Recommendations are greatly appreciated in assisting us with improving your overall customer experience with QuickBooks Online.

If you have any other questions, feel free to reach back out.  We'd be happy to assist!