I have two RLV430 thermostats, one in each of two bathrooms, running electric baseboard heat. Both have one inch to two inches of black marks on the walls above the right side, control pad; almost as if something had or is slowly burniing. Suggestions?

I don't like the sound of that! Cut their power, and carefully remove them to see if anything is burned behind them.

Just so you know few things in a persons house us as much power as 220V electric baseboard heaters so it is imperative you get to the bottom of this.

Sounds like an overheating condition. This could be caused by deteriorated thermostat contacts or loose wiring causing a high resistance in that area which will lead to discoloration of the area due to heat generation.

By any chance do you smoke in these rooms? I have the same problem in my garage, I just switched it out for a new thermostat just in case, but the mother in law smokes in there and as they do produce some heat it may just have been the nicotine moving through the ventilation holes??