Creating Mesh Decals
Creating texture decals can take some time unless of course you have some ready but then you still have to deal with UV’s.
There is another way if you don’t want to cross software and save a bit of time.
You can create the decals as regular 3d meshes or as flat faces sticking to your hard surface models.
The basic operation would be to snap the 3d cursor to your main model, create a primitive plane, then going to edit mode delete the existing verts and then modeling the decal shapes using the snap to face function for the verts to stick to the surfaces underneath it.
After you're satisfied with the design, use Alt+S to offset the decal mesh just a tiny bit from the main model's surface so it will show up on render.
To make it easier you can use the Ice Tools Pro to do this as the Create Link Mesh operator is designed to automate the above steps.
You can even use the text to 3d object function to create words.
Then use something as simple as a noise texture to create a worn effect.
And finally, for the last step before rendering (Cycles) turn off almost all of the ray visibility options for the mesh decals leaving only the Camera toggle on.
This will disable the floater decals geometry to affect its surrounding rendering it only as a flat diffuse texture.
That’s it! With this simple method you can create your own decal without ever leaving Blender and will let you save time if you’re on a tight schedule where you’re only after some sample render results.