I need something to project a sprite without using (spot)light, because it don’t has to be visible in dark areas. Is there a way to to do that?
If you are looking on projecting shadows/coloring info on your scene from the sprite, I am not sure how to do it without using a light / light cookies:
If you are just looking on projecting a sprite like a decal on top of a plane surface you can use a simple blended (opacity) material on a plane, and position/rotate the plane to sit on the surface.
Unfortunately, the first option is not possible because it is visible in a dark environment, and the second option is not possible because it does not mold with the substrate.
Then you will have to study how decals / dynamic texturing works and create a shader system that can calculate UV coordinates on the fly.
This is quite advanced to put in place.