How do I create a backlit wayfinding sign?

I'm trying to create a backlit sign by using an emissive material with a custom decal with text placed on it. The idea is that the text blocks the light from the emissive material. When I try this approach when I place the decal on the emissive material, the decal is not visible.

Is there a trick to doing this, or a better method?

Thanks in advance,

AA

I would extrude the text slightly in my model so it is geometry rather than using a decal.