OK, so its not the most exciting picture but seen here is a good example of properly finished mortar joints.  The blocks have had the sharp edges removed with a mason's stone.  The mortar is recessed back into the joint lessening the exposure to sun and rain which prevents early failure.  There is no mortar on the face of the stonework spoiling the wall.  These mortar joints have been properly pressed/tamped during the construction phase, not just trowelled in.  This removes the air and water such that the mortar is consistent in texture, without any defects or pockets and ensures a long durable life.