Hi there, @rschaffer. Thanks for joining the thread.

Right now, able to add e-signature to checks in QuickBooks Online (QBO) is unavailable. 

In the meantime, you can affix the signature manually on every check you’ve printed as suggested by my colleague PreciousB or integrate a supported E-signature third-party application. Since QuickBooks integrates with hundreds of third-party software developers.

While I’m unable to recommend an app, I can route you to the website where you can look for an application specific to your business needs. From there, you can integrate the app to QuickBooks Online (QBO). 

Additionally, to view a wide range of options, use specific keywords to narrow down the search. You can check the reviews from other customers to help you decide which app suits your business type and needs.

Let me know if you have any additional questions by using the Reply option below. I'm here to ensure your continued success. Have a great day!