Sigilian Currency Exchange
Sigil, and most of the Planes, use their own monetary system which is different from the Prime Material Plane's. Prime characters will be unaffected by this switch - starting gear is purchased as normal. However, they will then have problems once they get to the Planes and attempt to purchase additional equipment.
A simple 1'' diameter copper disk inscribed with the Lady of Pain's symbol on one side (2 grams). A 1'' diameter coin made out a permanently rusting metal; gives the appearance of being covered in dried blood. Feels warm to the touch (3 grams). A 1.5'' diameter silver ring with 4 crossing silver bars inside, thus resembles a barred window (10 grams). A 1'' diameter sphere made from a white marble; glows with a faint light when touched. Feels cool to the touch (10 grams). A massive, 1/8" thick, 3'' diameter gold disk with the Lady of Pain's symbol inscribed on both sides (120 grams).
It should be noted that certain areas of the Planes will have their own local monetary system which will take precedence over this system (Larvae in the Lower Planes, for example).