TIPS:

Autograph Abbreviation List

Autopen

Celebrities will sometimes use a machine that is set up to duplicate their signature.  These are not always easy to spot.
BW, B/W, b&w, etc. Black & White
C Color
COA Certificate of Authenticity
FOE Forwarding Order Expired
HOF Hall Of Fame
I Inscribed or Personalized
IC Index Card
IP An autograph obtained in person
ISP Inscribed Signed Photograph/Picture
ISPC Inscribed Signed Postcard
PP Preprint - photo of a celebrity that was signed once and then reproduced with the signature already on it.  NOTE: you can usually tell a preprinted autograph by tilting it towards a light source such as a desk lamp.  If the signature blends in with the photo, it's a preprint.
RTS Return To Sender
SAE Self-Addressed Envelope (no postage)
SASE Self-Addressed, Stamped Envelope; usually a 9x12 sized envelope
SC Signed Card
SIC Signed Index Card
SP Signed Photo, no inscription
SPC Signed Postcard
TCS Trading Card, Signed
TLS Typed Letter Signed By The Star
TTM Through The Mail