You write ~ before an address on an envelope when you are sending it to someone who is staying or working at that address, often for only a short time. ~ is an abbreviation for ‘care of’.
...Mr A D Bright, ~ Sherman Ltd, 62 Burton Road, Bristol 8.
C/O
Meaning of C/O in English
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012