Double Letters

I saw several examples of 3D letters used to produce 2 different words depending on the side from which you see them. I tried to check the web to find more ideas and realization but I don't know how to explain what I'm looking for.
The first time was a few years ago in an exhibition about optical illusion. The object in the middle of the room was just some lines with no meaning. But when you turn around suddenly you could read YES, and if you turn more on the other side it was written NO. Of course for this art project the meaning of not mistaken a "Yes" for a "No" and all the judgement and misunderstanding between people was very important. I'm focussing here on the techniques that make it possible (we are makers here).
More recently a colleague of mine saw one at the entrance of a company, from one point of you you can read "Welcome" (which is quite usual when you arrive somewhere) and from another angle you could read the name of the company. I started to think that I could do so