I agree with it being a poorly marked speed table (we call them speed humps in San Diego) But it is by no means a speed bump. Speed bumps are in parking lots, are small, steep, and there to make you go really slow like you should in a parking lot.
Forget about all the talk of expensive lawyers and such, you already know you're not going to go there. Get an estimate to get the damage fixed. Get online and find the phone number for the city streets division and call them. Tell them what happened and how much it's going to cost to get it fixed. Be polite but be firm that it's a poorly marked hazard. Getting angry isn't going to help you here if the person on the phone is not the correct person to handle this ask them to transfer you or give you the number for the correct person. You never know, the person on the phone might ask you to send the estimate in and the city cuts you a check. Then again they may tell you to pound sand. Point is you'll never know until you try.
As far as the pictures, I would refrain from sending them if possible. the frame damage is clearly not new and the speed table is marked, albeit poorly as if by a child with a can of spray paint. If you have to send pictures I would send the pictures, but also include a picture of a clearly marked speed table in the same city as a comparison of what drivers should expect.
