Are there outward signs of a French drain?
To tell the truth a really good French drain install will have no evidence with the exception of the water exit point. In some cases you may see a brown stripe through the lawn but not in all climate zones. A stripe that is brown is one way to tell but not always there. It is much like a leach field in some areas they are green above the drain field and some are brown it depends on the soil and local clean mate and rain / heat.