Yes, you can use BBCode when writing Forum Topics or replying to Forum Topics in Groups.
Bulletin Board Code or BBCode is a lightweight markup language used to format posts on many popular message boards. Tags are usually indicated by square brackets surrounding a keyword, and they are parsed by the message board system before being translated into a markup language that web browsers understand, usually HTML or XHTML.
Below are some examples of BBCode:
[ b ] bolded text [ /b ]
[ i ] italicized text [ /i ]
[ u ] underlined text [ /u ]
[ url ] http://example.org [ /url ]
[ url=http://example.com ] Example [ /url ]
[ img ] http://www.link-to-your-image.com/images/file.jpg[ /img ]
[ quote ] quoted text [ /quote ]
For more information on BBCode, visit this Wikipedia article HERE.