A special courier drops off a number of envelopes in the mail slot that eventually find their way to their various recipients. The envelopes are a deep red with a golden border and addressed to peoples' full names in elaborate handwritten script. Inside is a placard that is deep red with an intricate crest on the backside and this on the front:
((If your character is over 18 and you're interested you can chose to have received an invitation, though it helps if your character has at least a little bit of a reputation.))