One thing about some railroads as they were built in the 19th century, they were frequently incorporated and chartered separately in each state. Even though a railroad operated as a single entity, their various parts may have also used separate reporting marks as subsidiaries.
S.P.C.A.L. could stand for the Southern Pacific of California, Inc. in this case. Perhaps there may have also been some tax advantages to that at the time when those tank cars were purchased. Also back then it was customary to put a period after each letter in a reporting mark, even if some letters might be for an abbreviation. Later revisions of regulations limited reporting mark initials to four letters.
Ed Bommer