the only "watermark" is the aximmetry logo on the bottom right. what you are seeing is the touch interface controls. this can be disabled in your unreal engines project settings.

Thank U. Emm, I think so. But where?

@liaobs: For future projects, I also recommend starting with a non-game template to avoid having to deal with game specific things like this. A very simple one comes Aximmetry UE5 editor, but the Arch Viz templates in the main UE5 installation are also very useful.