BTWs, in letters

• Some email enders
• Add-on endings in a letter: Abbr
• They're not part of the body: Abbr
• They're usually under signatures: Abbr
• Notes added to notes: Abbr.
• Postscripts: Abbr.
• Supplementary words in a letter
• E-mail endings, at times
• Last-min. additions

Wikipedia Word definitions in Wikipedia
PSS may refer to: