Matte Black material suggestions

[Jdylan423]

I have a project to create a sign that needs to be 25" x 25" x 2-3 inches deep with 4 letters CNC engraved 1.5" into. The sign will be displayed outdoors.
The color needs to be matte black and be able to be cnc routed. Of course, it can be any color and I can paint it with auto paints. A solid block of some material would be ideal.
Any suggestions on materials that would give me that depth and hold up on weather? Thanks
I attached a picture for style reference.

 

[CanuckSigns]

HDU

 

[Jdylan423]

HDU

Any idea where to get HDU in the USA?

 

[CanuckSigns]

Any idea where to get HDU in the USA?

any sign supplier that sells sheet goods should have it, i'm not from the states so I don't know specifics, it's sometimes called sign foam