Preheat a grill to medium-high heat.
Cut pears into thick slices (4 to 5 per pear). Place slices evenly in a large pan or bowl. Melt butter in a small saucepan over low heat. Pour melted butter over pears. Add brown sugar, cinnamon, and vanilla to pan and mix until pears are thoroughly coated with the mixture.
Place pears directly onto hot grill. Cook for 3 to 4 minutes on each side. Remove pears and place in individual dessert bowls. Pour remaining butter mixture into a medium, grill-safe saucepan. Place saucepan on grill and cook, stirring, until boiling. Remove from heat.
Place 2 scoops of vanilla ice cream over the pears in each bowl. Pour butter sauce over ice cream and serve.