The Key System may once have had reporting marks for its freight switching operations which served industries mostly in the vicinity of the north side of West Grand & Adeline Sts (a lot of the tracks were still in the pavement as of about 4-5 years ago, along with the white Xs hanging from what used to be overhead wire supports).

Before WWII there was a plan to develop what became the Oakland Army Base into an industrial park, and some of this trackage was actually built for the Key's use. The Railway Equipment and Reality Co, Key System's parent company, sold the rights to the switching operations in the 1930s to a combination the AT&SF and WP, which used the OTRy (Oakland Terminal Railway) name, a shortening a shortening of San Francisco-Oakland Terminal Railways, which dates from very early in the Key's history. One of the reasons the OT has always served industries on the west side of the Cypress St freeway was because of the pre-war industrial park (the name "Parr Terminal" comes to mind, but it's been a while since I saw the map). ISTR that the tracks along west side of Maritime St. leading from W Grand all the way to 7th St. are some of these. Thus, any time you see pictures taken after about 1934 of Key System and SN freight locomotives operating on Key System tracks, it's actually the OT, leasing the locomotives.

The transit operations of the Key System, by whatever names it was known by over the years, never had AAR reporting marks.