talkmagic.co.uk

Just got myself a packet of bicycle marked 1800 cards. They are fantastic, my pack is the blue ones but in the pack is a red backed QC does anyone know what this card is for.

It is a sample card for the sister deck of that colour. in your case a red deck.

Thanks.

It's a useful card to have if you know a card trick that uses one card of a different colour.

After the standard 52 the print run allows for 4 extra cards per deck at USPCC, in a standard pack of cards this would be two jokers and two advertising cards.
Many packs aimed at magicians will have an alternative to one (or if we're lucky) both of the advert cards that can be used in a card trick.