The pics show both sides and how deep, also found a another piece with it, not sure if they go together. Did some cleaning but stopped, didn't want to break it.
You didn't mention the dimensions, but you did say that you "didn't want to break it", so I assume it's pretty thin.
Looks to be painted onto stamped metal... so maybe a part from a child's toy, possibly a pedal car, a wagon or a tricycle.
I'd say c1940s - 50s based on the color.