Q:

Is InitializingBean and DisposableBean marker Interface?

Marker interface means interface which have no methods. Then why we call the  InitializingBean and DisposableBean interface as a marker interface, even though it has afterPropertiesSet() and destroy() method respectively.

A:

It is not, and spring open an issue that was fixed by renaming from marker to callback interface

I've used the term "callback interfaces" there now. 

Original text taken from excerpt from the 3rd Chapter of the official Spring Framework documentation:
3.5.1. Lifecycle callbacks

The Spring Framework provides several marker interfaces to change the behavior of your bean in the container; they include InitializingBean and DisposableBean.

