The "10" should be "10 units", whatever the unit of measurement is. It means the radius of the round is. Rounds typically try to create a tangent to the pair of surfaces that intersect at the selected edge. They typically do not "report" a centerline or axis.
Arcs can be dimensioned with radius (one click) or diameter (two clicks). Again, the value reported is the radius or diameter in the unit of your part.
When you simply edit the value, you will not see the diameter or "R" symbol, but when you look at the dimension properties, it will have the symbol in the text attributes as a prefix. You also see this if you show the dimension annotation in the model or on drawings.
There are several ways to show the centerline of an arc typically when you extrude or revolve a sketch. There is a special setting in config.pro that also allows you to create an axis when you extrude arcs that typically would not create an axis. You can also create a datum axis using any cylindrical or conical solid face or surface.
This is presuming you are using Creo Parametric, or course.
