When working in SOLIDWORKS Composer you will notice that there is a Dassault Systèmes logo on the SOLIDWORKS Composer Viewport Ground. If you want to remove this, or change it to something else you can.
To change the image to one of your own, go to: File > Properties > Default Document Properties > Viewport. Just below the Ground checkbox there is an area where you can change the texture path. If you want to remove the symbol, you uncheck the Ground option.