Knowing that in the process of using Digital Signature on Mac, you have met a difficulty that the PDF Icon can't be removed. You can try the following to solve your difficulties.
We believe you have already known how to add a digital signature, you can follow the previous process again. But, if you forget, you can check How to Add Digital Signature to a PDF.
When you have completed the previous steps, you can follow the next steps.
1. After creating the digital signature, select the one you want to remove the logo from;
2. Click Continue and select the Edit icon in the upper right corner;
3. Check the Logo, remove the PDF icon, and click Continue.