Perfectly symmetrical shapes are created easily by drawing half of the shape, duplicating that half, flipping it, and then combining the result. However, combining the path into a single shape requires precise alignment, or use of a little trick that overlaps the elements. So long as you know what to do, either of these is easy, but if you don't know what to look for, the end result could be not quite so perfect, and the effect can be ruined.
Once the shape is created, it is easy to store it in the current Shape set. From there, it can be Retrieved and applied as a custom shape in any image.