It’s easy. Doesn’t matter what you’re adhering it to. You just import the OBJ file into the scene. Once it’s there, arrange it to where you want it to sit on the character. Press it just barely into the suit, and then parent it to the chest, shoulder, whatever.
If you want something morphable like Superman or Batman’s shield, then that’s just a matter of taking the mesh and painting the symbol on it.
So, for instance, if you have a shirt, any shirt. Make a copy of its chest texture. Then take that copy into a paint program like Photoshop and apply your symbol. You can then put that texture into a folder (I have one that’s called MY TEXTURES) wherever you’ll remember it and go to the Shaders section, click on the “Texture” file and choose the new file. Done and done.