Take the situation listed in this question:
Mapping multi-Level inheritance in Hibernate
How would this mapping be done with Annotations rather than an hbm f
Inheritance between @Entity annotated classes is picked up automatically. So if you class A is annotated and class B is also annotated with @Entity and extends A, and C extends B and is also @Entity annotated all will be picked up.
I have not used joined subclasses combined with discriminator values, but I'm sure it will be very similar to what is done in XML (using @DiscriminatorColumn and @DiscriminatorValue)