Is this a NZ Potter and if so who?

Wondering if anyone can identify this makers mark? It's either an S over an M or a W over an S inside a small circle. 



 https://i.servimg.com/u/f77/20/39/16/58/20211211.jpg

 https://i.servimg.com/u/f77/20/39/16/58/20211210.jpg

I'm sure this is NZ pottery, although after a quick look in the Potters Marks Gallery it didn't show itself. I will have another look later.

Thanks to the Ferret for letting me know that this mark belongs to Stephen McCarthy

https://www.newzealandpottery.net/gallery/New-Zealand-Potters-Marks/MNOP/mccarthy-stephen-pic_9782.htm

Oh thank you SO much for your sleuthing! Fabulous to know. I wonder if there's a way of tracking down when they were made based on what mark was used. They seem to have changed over time.

Am contacting Steve for information. Will get back to you.

Oh cool. It's hard to find info about him in Google.

Stephen McCarthy says he is unable to help identify these pots but they are definitely not made by him. He used a stamp with a capital S over M in a vertical oblong and only during the early part of his life as a potter. He found the stamp was either clogged up or he couldn’t find it. After that he didn’t use a mark. He used coarse stoneware clay and not white porcelain type clay like these photos.

Wow!!!!!  Thank you so much for contacting Stephen.
On Monday I couldn't even find the post from the Ferret where that mark was identified, so I won't be able to correct it.  
However I will add it to the Mystery Marks and keep looking for the post.
Well done and thanks again !

Edits to say that I found the post and the mark was thought to be the same as the one in the Potters Marks book, but it isn't and I have corrected the post.