Other hobbyists have contributed helpful suggestions, and you may already be moving forward with those tips.
I considered lighted toggle switches for identification on four stub sidings on my L-shaped layout, but installed a different "solution." I placed four unlighted toggle switches in a project box at the control panel and activated the sidings with them. Then I installed a lighted Lionel bumper at the end of each siding. When a toggle switch was ON, the bumper light at the stub siding was also ON and served as an indicator. Readily noticeable for me to see as an 81 year old -- and probably useful to your dad!
Mike Mottler LCCA 12394