This is the Sega Diamond Star, taken from a book showing different Sega slot machine models. According to this manual I just got, this slot machine was made in 1959. OK, whatever. Note the Sega Incorporated, which makes sense for a pre-1965 advertisement. This proves that the Sega script that the Sega Retro logo uses is at least older than the formation of Sega Enterprises. However, that's not really what I'm interested in. There's also the "Sega" script on the slot machine, but this isn't really interesting either—I'm guessing this is a rebrand of a Mills slot machine given the date and they just made a piece that fit where one would place the Mills badge.
You can tell that part of the page was cut out and replaced with that "Manufactured by Sega Incorporated" logo. I think that may be an updating of an older logo still.
This logo was on the front of the slot machine manual, which has a print date on it of November 1962. Normally, I would shrug it off and call it something custom done for the manual, except this isn't the firs time that I've seen that styling of Sega.
It's an exact match of the dial used in Punching Bag. I confirmed the date of that machine to be 1968 by reading through Billboard Magazine's archives (they had a weird interest in covering coin-op stuff from 1945 to 1970, so if like to read about inane details like where Irving Bromberg went on vacation, check it out.) With that, I'm now more confused than ever about what the first Sega logo really is. Just thought I'd share in hopes maybe someone else can help me on this.