The Sign by the Road

Does anyone actually phone a contractor, painter or roofer, based on a sign shoved into the edge of a lawn? Who are these people that, when driving along at 60km/hr, can not only read the two-foot sign that's perfectly parallel to the road, but can fully recall the phone number at a later date?

Maybe someone in the trades can correct me, but unless you're aiming your services at those with great memory and eyesight who have a tendency to look out the passenger's window whilst travelling at high speeds, this seems an extremely ineffective way to advertise your services.