Here are some mystery signs!
These signs appear to be made of solid plastic in 2 layers. They have a metal peg on the back for hanging. The curious thing is there's no markings on them at all.

These are likely to have been store signs of some kind, like for displays. They measure 37 centimeters wide and 29 centimeters high. One is the Sonic Team looking logo, the other is Sonic X. They were likely chosen because they are sihloutte style and able to be cut/made simply enough with just 2 layers. As you can see the plastic for each is pretty thick. Even though they're mysterious / unmarked, they're a cool collectible to have on a wall in a Sonic room.