Quote from TeamSpen210 on June 1, 2014, 4:41 am

When looking at the turret_skeleton.mdl/defective turret model, there's a large blue box in the middle part of turrets (presumably hidden in normal ones, but not rendered). On it is the words "Fusion Core" and "Power". Apparently Aperture Science has miniaturised nuclear fusion technology! Perhaps that explains why the reactor didn't run out of power after the 9999999 time skip, although they'd need to have fission reactors as well for the "Reactor Core Meltdown" the Announcer mentions a few times to be possible (Fusion reactors should not be capable of meltdowns like fission reactors do.)

Additionally, there's some very pixelated text above the "Live Ammunition" hoppers on the upper part of turrets, it seems to be disarmament instructions or some similar warning.