During the course of your home inspection, the home inspector will tag all of the Gas and Water valves in your utility room. These tags are meant to provide the home owner easy identification of all valves in the event that they would need to access them.
Let's say for example one of the teenagers comes home from school and notices the water heater is leaking profusely and running down the floor drain. They call dad at work in a panic and ask what to do... of course dad is perplexed that a teenager was in the utility room.. perhaps doing laundry? Anyway, he explains that they should shut off the water and gas valve at the water heater. If they are tagged this will help make sure that the proper valves are shut off.