When reading tarot cards, it's sometimes helpful for the reader to choose a specific card to represent the readee. This is called a "significator." There are other contexts in which I've found it appropriate to pull a significator for someone, which is kind of ironic -- I don't generally use them for actual readings, save for the relatively rare occasion when I'm performing them long-distance.
There are a couple of ways to choose a significator, a few of which have to do with astrology. To illustrate this, let's look at a hypothetical older man born on June 14th. That would make them a Gemini, which is an air sign. As every tarot suit has its own corresponding element -- Pentacles for earth, Cups for water, Wands for fire, and Swords for air -- you could choose the King of Swords to represent this person. The major arcana card "The Lovers" is also associated with Gemini, so that's another option.
Sometimes, the physical appearance of a person can play a role in your choice (especially if you don't know what their astrological sign is). Say our hypothetical man naturally has light hair, light eyes, and fair skin. Cups might be a good choice here, as it corresponds to people with fair to medium skin, light brown, blonde, or gray hair, and gray, blue, or hazel eyes. Since he is an older man, the King of Cups would be the likely choice.
[caption id="attachment_3363" align="aligncenter" width="513"] Pick your poison. The King of Swords? The King of Cups? In this case, the King of Tools may be more appropriate.[/caption]
Depending on the situation, it's also appropriate to pick a significator based on the person's role or situation. If this man is a manipulative individual, The Devil is a good choice. If he is an authority figure, perhaps The Emperor would fit the bill.
So, once you have a significator, what can you do with it? Many tarot readers set them aside to sort of focus the reading in question. I've done this when I'm performing a long-distance reading for someone, but I mostly do in-person readings. Tarot aside, there's another purpose that a significator can serve -- as a focus for magick.
A lot of spells, whether they be helpful or baneful, require the use of a taglock or personal concerns. (I talked a little bit about personal concerns here.) Sometimes you don't have access to someone to obtain these things. If someone far away is threatening your well-being or way of life, for one, you may not be able (or even necessarily want) to get close enough to obtain a hair clipping, old shirt, or what have you. If a long-distance friend is in a tough situation and you want to offer them some supportive magick, there may not be time for them to send you a taglock. I've used a significator card as a stand-in for the objects I don't have.
A taglock isn't always necessary for directing magick, but it helps. If you don't have one to work with, use what you have access to. A lot of witches I know have tarot cards around, so choosing a significator card makes for an easy and viable alternative.