Tarot cards date back to 1390 in France and a tarot deck has 78 cards. There are 22 cards in the major arcana and 56 cards in the minor arcana. The minor arcana consists of four suits which are the pentacles, wands, cups and swords. There are various spreads and many ways of reading the cards. Each tarot reader is slightly different. Some use their psychic abilities when doing a reading and others merely look at the cards and let the thoughts and imagery flow. The cards can usually convey their messages well.
Many readers do not use a signifier but others prefer to. It is a matter of personal choice and you might prefer to try reading both with and without, to see which method suits you the best.
A tarot Card signifier, also known as a significator, is one card chosen from the pack to represent the querent (person you are reading for). A signifier is almost always a court card (king, queen, knight or page) and represents the temperament, age and coloring of the person the reading is for.
Kings and queens are usually people over 36 who are, or have been, married. Knights are younger and Pages can represent children of either gender.
Another way of choosing a signifier is to match only the physical characteristics of the querent so, for example, the King of Pentacles could represent an older, dark-haired male. You could match the personality too. The Queen of Swords perhaps could represent an older female who is stubborn and has strong beliefs. Different readers use differing systems. Some use only physical characteristics, some only age and hair color and some have their own systems altogether. The tarot is a very personal thing so whatever card a tarot reader chooses to be your signifier, that is their choice and will produce the best reading from them. There is a lot of intuition involved in selecting signifiers. Sometimes one just feels right even if it has the wrong color of hair or is in the wrong age bracket. You should always go with hunches when it comes to reading the cards.
The good thing about using a signifier is that it guarantees the reading will be only about the person asking for it, as you focus on the signifier whilst performing the tarot reading. However, it does take one card from the tarot pack, which might otherwise have been in a key position with a message. For example, if in a reading you get the Page of Wands in a spread, that card can mean that there is a creative restlessness within the querent and it is time to begin a project. If you are using the Page of Wands as a signifier, that card will not be able to appear in the spread. Other cards can convey similar messages but that is one thing to bear in mind (unless you use a second tarot deck for the signifier cards).
There are reasons for and against the use of a signifier and it does very much depend on the reader and what he or she is comfortable with. Being comfortable and happy with the manner of the reading usually ensures the best results.