This is where SSRS Security Manager excels. You can see where there are differences in security.
Using report manager to look for security differences would mean going through each item and looking at the security of every item, how long would that take? What are the chances of missing an item?
The icon is yellow indicating the security of the folder is inherited but there is an item in the folder that has different security (not inherited). In the above example DataSource1 is highlighted red to indicate this items security is not inherited. It is recommended only to change security on folders not items in folders. See SSRS Security best practices for further information
The icon is red indicating the data source called DataSource1 is not inherited
The icon is red indicating the folder DataSources is not inherited.
The icon is green indicating the Report Project 1 folder is inherited.