https://www.google.com/search?q=WF+mark+on+studio+pottery&rlz=1C1SKPC_enUS366US455&espv=2&biw=1280&bih=709&tbm=isch&imgil=f54urY2WdhOrtM%253A%253BuMBQL919rw6bnM%253Bhttps%25253A%25252F%25252Fwww.pinterest.com%25252Fokayok%25252Fstudio-pottery-chop-marks%25252F&source=iu&pf=m&fir=f54urY2WdhOrtM%253A%252CuMBQL919rw6bnM%252C_&usg=__Z23HuD5mvWSTT4R1v9UDgKjMx8g%3D&dpr=1&ved=0ahUKEwi_wcCq2MbQAhXGrlQKHa9VBaUQyjcINQ&ei=6KM5WL-tNcbd0gKvq5WoCg#imgrc=f54urY2WdhOrtM%3A

I think the letters are a conjoined WF !! This is a studio pottery and the link is just to give you an idea of the difficulty in finding one maker in the thousands there are !! I have not found any using that type mark !! I am still looking !!