Looking to replicate the Queaker logo effect

Greetings to all! I humbly request your assistance. Recently, I created a portrait logo for one of my clients and decided to take it up another notch by including an added effect on the design using Photoshop. I already finished the vectorized version but I am unsure what is this exact effect on the quaker logo guy

. If anyone could kindly offer some suggestions or even sources for guidance I would highly appreciate it!

It’s a registered trademark so whatever you are doing, then I would suggest you proceed with some caution.