lettering / stencils on m116a1 trailer

[johan77]

does anyone know what these number and letters mean on my m116a1 trailer? the vco number should be the registration number but the ones i red and ADU is still not clear what it means or stands for.

 

[steelandcanvas]

ADU = Air Defense Unit?

 

[johan77]

could be, but would be a bit strange because the trailer was loaded with a generator set...