what are all those markings on baby sunstreaker?
As a new spark he was sold to scientists to experiment on the bond with. When they no longer needed him and his brother they sold the twins to a slave ring.
He was the 115th mecha aquired on the Solar Solenoid, as such he was branded with taht informationa nd that is what his 'designation' was to those that bought and sold him and his brother.
His right side has the branding of being a gladiator (there are other brandings for Pleasure bots, Dancers, Runner/Mules, etc.) and he belonged to the Kaonite Pits (the mark next to the branding). Old owners (on his left) are crossed out and the new ones branded on. AS he grows older if he makes it and if his owner so chooses to upgrade him his frame will be melted down and remade with other materials, removing old brandings and the current owner will restart the the brandings.
The scars are from previous battles. His optic was ruined and replaced with his opponents, and his audio wasn't worth the owner replacing it.
When he hit half majority the owner that had him had his protoform melted and replaced with a more durable material as they'd seen his worth in the pits and knew if they could bulk him up and make him sturdier he'd continue his winning streak and it was an investment worth it to them. (Sideswipe had similar upgrades, just havent drawn him yet!)
SunStreaker (double SS like the branding) Named himself and SidesSwipe (double SS like the branding) in the pits. So while they were called and labled SS114, SS115; they had their own names for each other.
This is based heavily on my written Barbarian AU Where Sunny and Barbarian Jazz end up bonded; Sideswipe and Barbarian Prowl end up together.