How to recognize by only looking the name whether it is a class or an interface?

Answer 1

It was a common convention to use the uppercase letter I as a prefix to name interfaces. I think this convention is kind of deprecated, because you just have to hover the mouse over a name to see its type when using an ide.

Answer 2

In C#,

Class names are written in "Capital Letters".
Interfaces names are written with beginning of the character is capital "I" so we can know it is interface. For e.g.

public class Class{}

public interface IInterface{}