Here is an interesting sign! It is likely uncommon as well.
This lights up (here, it is seen plugged in & turned on) It is basically tube shaped. The front has a big 3D Sega logo, with curved back to fit to the rounded sign. There's also a Sega logo raised in the blue plastic on both ends. The front has Sonic, Tails & Knuckles. They're on the usual checkered ground, with a simple blue/gray background. But look at that crazy looking Robotnick there! What's going on with him? He is sort of 'ghostly' in that the image is sort of transparent, his gloves are not attached to any arms, they're sort of just...floating there by Knuckles in a "Scheming Hands" position. Then, he's looking right (instead of left, to menace the heroes) but his eyes are white instead of red. (Clearly they printed in red...Knuckles...) so why the error?
This sign would probably be seen in game stores, or even game sections of larger stores (like Toys R Us, etc) because back in the days of Sonic 3 & AOSTH (the show) where it looks like this Robotnick graphic was from, toy/game sections & retail toy shops were more common. You can see it's pretty big too, it's sitting on a regular sized sofa in these images. It is now in a personal collection. 

In the image gallary you can see what happens when you take it out of the tube. It has the exact same look & color, but can be removed from the Sega themed light up tube. Look at the measuring tape, it is about 2 and 1/2 feet long.