Frame and tie down damage from unmarked speedbump.

Looking at your picture I see exactly what you describe, an asphalt speed bump a few inches higher than the surrounding pavement. Have seen them before. And unmarked they do blend into that pavement. And yes, they are typically clearly marked. I am curious what the diamond shape warning sign about 3 car lengths before the speed bump says though.

Not likely you will get anything at all from the city.