Well, there's a question of what did the North Shore, who built the electric interurban operation in southern Marin, use for it's markers and what not. In the pictures they look pretty much like the concrete examples that are extant. However, hard to tell if they are concrete are wood. Maybe I coudl look closer at some higher res photos and see if I can tell if the lettering is stamped or just painted on.

By the way, the North Shore, while not known for sure, is said to have been a Santa Fe-SP railroad from the start, or planned to be eventually bought by that consortium, if that's the right term.

But the extant whistlepost is from Tiburon. And then there is the one from San Rafael which disappeared during the SMART construction effort and hopefully was not thrown in a dump.

Will be interesting to continue the research into what appears to be a least minor interesting issue of mystery