The Geoffer clan has shrunken greatly. At present only 7 members exist, including those by marriage or invocation.
The true nature of the Geoffer clan is defined best by Bluenose Jackson Geoffer as being:

An official list, an official mark.
An official family to officiate bonds of love, friendship, and loyalty.
Our friends are one and the same. Our enemies are one and the same.
We share our greif, we share our joy. The only thing we don't necessarily share is our blood.
The Geoffer clan is close-knit. The Geoffer clan is not always related.
Take my hand, clan-mate, and we shall share in our frienship.
We shall hunt together, we shall weep together, and mostly we shall laugh together.
Let it always be as such. Let us always be bonded by head and heart.
The Geoffer clan is closer than blood. The Geoffer clan is bonded by soul.

Bluenose has made a very good statement. He has put his claw right on the mark. The Geoffer clan is not bonded by blood as much as they are bonded by kindred souls and a similar path through life.
The clan sigil is simple. A golden-yellow tiara, the mark of loyalty, with a simple red diamond of courage in the center. Whether or not it is magical is still unknown by even the clan-members themselves.
The present leader of the clan is the youngest member, Niña Wolfganng Geoffer. The other five existing members are in hiding and count on her to carry on the clan tradition. Since the clan has almost died out, the old clan enemies and friends ignore them, and some are even convinced that they have died out.
Marriage within the clan is not unheard of, and was actually fairly common due to lack of blood relations within the clan until their downfall. Some more traditional clan-members refused to marry outside of the clan, knowing what kind of traits clan-members had to exhibit. Due to familiarity with these traits, clan-members frequently decided that ideal mates were to be found within the clan itself.