I FOUND A SOLUTION!  This might help some of you.

I was able to add an "image watermark" to my home office printer, an inkjet Brother.  It took a short while to position and scale my signature image, but now when I print my checks, the signature is automatically there.  It only prints on the saved profile I use for checks so it doesn't show up on any other of my printouts.  QuickBooks Online should have this functionality, but maybe you can add it to your setup like I did.