@Michael-Angelo-Go Well done on getting your shop up and running. Ness is right about watermarks needing to cover the whole image. It's easy to remove them. Here's an example from the pic you posted. I just used the lasso and content aware button and used healing tool on the back paw. So that was the computer doing all the work. Took under a minute.
I personally wouldn't bother with watermarks unless selling for stock images. They distract the eye from the image underneath. Signatures are best used on limited edition artwork or for selling originals (signed in pencil or paint). If it's an open edition I wouldn't sign it.
Plus a digital signature can be lifted off and then placed on other art to pretend its made by you.
For a digital signature, make sure it's not the same signature you sign cheques or credit cards with! 😃