Basically printing 3d letters for indoors (or outdoor) like on the picture? Is there a special printing technique involved in the making of these letters?
There is no printing technique for this but these are custom made letters. Based on the pictures I would assume the top are metal letters possibly formed and painted at a lighted sign shop. The bottom letters, based on the texture in the light, appear to be foam letters. There are many variations to 3D letters. A simple google search for the following could help you narrow down the type of letters you may need: