The difference that a proper joint detail can make to your project can be significant. Often it is decided to use a “restoration” joint which will match worn look of 100+ year old mortar. However, if this is done it can often mean that in time there will be no existing record of the type of joint finish originally utilized. Whether the joint is double struck and ruled or weathered, birds beak or overhand struck, here are some common joint details that were often used in historic masonry.

WEATHERED: The weathered joint detail is achieved by taking your trowel and running it just inside the top of the mortar joint. The functionality of this joint is that there is no "lip" or ledge in which water can stand. It is very efficient in shedding water.
FLUSH: This joint detail is achieved by merely cutting the mortar joint off at the same level as the faces of the masonry units and then "slicking" the surface. Efficient for water shedding and easy to achieve.
OVERHAND STRUCK or "Struck": The opposite of the weathered joint detail, overhand joint finishes get their name by the masons who were working on the interior of the wall and would strike the exterior joints by reaching and working over the wall. This joint was commonly used in general construction on historic brick structures.
DOUBLE STRUCK or "Overhand Struck and Ruled": A combination of the overhand and weather joint details, this finish was a common decorative detail mostly found on facades or higher end buildings.
RULING: Ruling was often a detail that was applied on top of a finished joint, often to receive a more formal treatment, like tuckpointing or penciling. This is achieved by using a piece of wood as a guide and using a traditional "jointer" to run an indention into the finished joint. Here you see ruling illustrated on an overhand struck joint as well as the picture at the top of the page.
CONCAVE: A more modern method of finishing joints, a concave joint is made by taking a convex jointer and tooling the surface. Alternatively a beaded or convex joint can be made by using a concave jointer which would produce the bead.