Input Special Characters in VIM

Special characters or symbols are called digraphs in VIM. But how can we input digraphs in VIM? In “insert” mode, press C-k and followed by , which is the digraph coded-key that you are going to input. For examples:
C-k oo • (Bullet)
C-k Db ◆ (Diamond)
C-k Co © (Copyright)
C-k Rg ® (Registered trademark)
C-k Pd £ (English pound)
C-k Eu € (Euro pound)
C-k Ye ¥ (Yuan)
C-k +- ± (Plus-Minus)
C-k >> » (Right double quotation)
C-k << « (Left double quotation)
C-k fS ■ (Black square)
C-k OS □ (White square)

The complete digraph coded-keys can be found by type command :dig, or :help dig for more details about digraphs.