You are better off with a bumpmap vs. what you currently have. Bump maps are far from sufficient in closeups and flat angles, but for a numberplate it should do just fine.
Displacement mapping is overkill, and can also have the side effect of looking "pixelated". You could compensate by creating a even larger map to be displaced, and refine the displacement quality. The numberplate is a pretty small area so one could argue the extra geometry doesn't really matter. But it is still a messy solution for clean shapes like characters.
I suggest you create the characters with a bold font and then bevel the edges. You may not need to make them bold though. That depends on how your bevel tool works.
Then move the geometry so only the front faces and the front-most bevels are visible and you can delete the rest if you want to.
This will give you great results since the bevel will pick up highlights.