Up and coming Colonials might want to check out this handy poster which gives friendly and handy tips to spotting a Cylon:
Do they ask questions about classified subjects?
Do they seem unusually strong, smart or self-assured?
Do they say God instead of Gods?
Have you seen them before, but you know it's not the same person?
Do you see them hanging around secured or restricted areas?
Do they seem to hear music that no one else can hear?
Do they seem unusually fearless, as if death has no meaning for them?
Do they exhibit sociopathic behavior around other humans, especially defenseless children?
Are they unusually adept, almost empathic, with machines?
Does their spine glow red when they get... excited?