Decal does not seem to be an option in my version of the properties panel of RhinoMac.
Has this option not been implemented yet?
Since I could not find the “Decal” option I then tried to do this via creating a surface, and giving that surface the texture map that is in fact the text (a jpeg) I wanted to add. However I could not blend that surface with the material of the box object. The result still looks like there is a flat object of a different material, albeit with the desired text, laying on top of the box.
The rendering side of Rhino for Mac including texture mapping and decals is all still in active development and changing often. I’m not sure what features will make it from Windows Rhino for v1 of Rhino for Mac. Decals may not make it as described in the Windows Rhino documentation.
With all that said, you may be able to get what you want now by using a transparency map to make portions of the color texture see through and thus revealing the material color which could be the same as the surrounding box. You may need to make a new black and white version of your texture map to do this. I haven’t tried it yet and your file/texture may play a role in whether it would work.
If you can use TextObject instead to make the text as surfaces and then position them just in front of the box, I would go that route instead honestly. I could probably come up with a way to achieve this now with Toucan but it would be confusing and the wrong thing to ‘learn’ since this stuff is slated to change.