I am designing a class diagram for scrabble game. In one of the classes, I have final variable declared. Can anybody tell me, how can I indicate a variable as final in the UML c
Declaring a variable/attribute final is implementation detail. So you don't need to specify it in your CLASS Diagram but you can follow the convention as suggested by eboix.
UML specification doesn't say anything specifically about it; so you can follow convention of showing it in ALL CAPS.