Is it possible to make your own custom 'common shape' rather than use one of the pre-made ones?
Where are these objects saved?
I've done this using a macro. Create the shape first and save to a specific file. Create a macro to import that shape. Create a custom icon for it too.
1. Stop Sign shape (Octagon from the polygon tool isn't rotated correctly)
2. Triangle - with point at the bottom.
3. Arrow - my arrow
4. 3/8" circle (common hole for signs)
5. Windhole for banners
6. Grommets for banners
I don't know of any way to make shapes that can be interactively changed in the way that some of the "common shapes" can be, i.e., by dragging the special handles on some of the arrow shapes.
If I just wanted to conveniently reuse shapes, then I would use Symbols.
Another alternative might be to use Trays to access assets.