Warns when "auto-connection slots" are used. They're also known as "connect by name", an old and unpopular feature which isn't recommended. Consult the official documentation for more information.
These types of connections are very brittle, as a simple object rename would break your code. In Qt 5 the pointer-to-member-function connect syntax is recommended as it catches errors at compile time.
This check simply warns for any slot named like on__, because even if you're not using .ui files this naming is misleading and not good for readability, as the reader would think you're using auto-connection.