Everyone should be encouraged to use the Scout Sign and recite the Scout Oath and Law. Often I see parents at meetings that just stand there, while their scouts are reciting the oath & law. Leaders should encourage parents and guests to join in. Parents should use the Scout Sign at home or anywhere. Scouting values are not exclusive to registered members at meetings and outings.
Family Scouting: https://www.scouting.org/familyscouting/