This character will appear on desktop every time you done modification to Windows Address Book which is utilized by Outlook Express. It is element of a security patch for Outlook Express for an error which could permit an attacker to run malicious code of option on a user's machine. Sadly there is an error for error repair also.

When you do changes in Windows Address Book file, Windows will create a backup of this file. The patch renames backup file to ~ and saves it in directory where you launch Outlook Express. Many people launch Outlook Express from a shortcut on desktop, so backup file gets located there.

You can delete this file but it is suggested that you back it up first as it is a backup of Windows Address Book. I would rename it to somewhat like addressbackup.wab so it is easy to identify it. Give .wab extension on it to connect file with address book.