This cameo is slightly confusing. There is a show called "Hi S-Cool Seha Girls". However, the word "Seha" is a combination of "Sega" & "HArdware" because each girl represents a Sega system. There's Saturn, Dreamcast & Genesis. They each dress a little like their console & wear a controler like thing on their head. It's mostly a CG show, but obviously they got the license for tons of Sega stuff, you can spot Sonic as an item at the top, the star-bumper ceiling light, Sega logo Space-Channel 5 (blue thing to the right) Opa-opa (green/red space ship & NiGHTS statue. Then, Sonic himself appears to run past the girls in CG. In the title screen, you can easily see a neutral chao. 

Because the show has the license, they actually meet Sonic in an episode. Eggman breaks the game "Border Break" while the girls are trying to 'play' it to earn medals (the point of the show / its plot) and sends robots to attack the girls. Sonic saves them & they end up riding around on his head while he tries to defeat Eggman. It shows scenes from Sonic 1, Sonic Adventure 1, and plays music from the Star Light Zone. Neither Sonic nor Eggman ever speak, they just gesture.