I've been collecting Porcelain insulators for over 35 years and the different shapes and markings always facinate me. I always try to attribute the markings to manufacturers and find some history on them for my own personal reference but some I've had little to none info found. This picture is of a company that is based out of California and where most of the insulators have been found. They are marked Sissell, a slanted S in a circle (not to be confused with Seyler Mfg. Co. S in a circle or Slater mfg. Co. S or S in a diamond markings), spools marked Sissell 201 and a M within a diamond which I believe is in some relation to this company because it has the same wire holder mold. The only info I could find on this company was an address for burial vaults made of concrete or precast. Here is a picture of the Sissell wire holders and a white plus grey spools made by them. Mike Green posted a picture of a beautiful brownish colored spool by them a while back. I would greatly appreciate any info or pictures you may have. One thing I have noticed is that there products were made with top quality porcelain and used brass lags in there wire holders which was an exspensive option for other companies.