If something is seriffed, it has serifs, which are the little lines at the ends of letters.
Seriffed letters are often seen as more traditional or formal.
Examples:
The seriffed letters in the book are very pretty.
I like the seriffed writing on that sign.
The seriffed letters on the computer look nice.
The seriffed letters make the sign look old-fashioned.
In the olden days, all writing was seriffed.
The seriffed letters on the poster are very fancy.