As seen in his driving license, John Constantine's age is given as 10th May, 1982 (which puts his age at 32 at the start of this show). It is also the same year in which Sting played an ambiguously demonic con man in the film Brimstone and Treacle, which led to Moore creating the character of Constantine.
Capnomancy (otherwise known as Libanomancy) signifies a method of divination using smoke. John uses this method to predict lottery numbers and procure money.
Most of Zed's drawings you can see in her home are famous covers or represent villains from "Hellblazer" comic.
Zed, the character played by Angélica Celaya, first appeared in Hellblazer #4 (April 1988)and was created by original Hellblazer writer Jamie Delano. She had psychic abilities which are reproduced in the show.
One of Zed's drawings, near her door as she exits, is of a four-headed figure. This creature, which named itself Ironfist the Avenger, was made from the bodies of four football hooligans and was featured in Hellblazer #6.