the sigil or "seal" of a spirit is usually traced in a circle and is the spirit's signature.
I am unsure of the ones you are specifically referring to but most of these are made with a combination of correspondences and intuitive drawing/ automatic drawing under the influence of said spirit.
sigils can be made with one word, yes. though often they are created from a statement of intent or a combination of other symbols with their own correspondences
Two more methods of creating the sigil of a spirit are with either a ring or a grid of letters -- often in the language native to the spirit's name, or that of the root of the tradition being used. Basically the practitioner plays dot-to-dot to spell the name across the ring or through the grid.
Let's say you're wanting to call upon, bind, or otherwise work with a spirit named Thomas (a common enough name chosen for this). Using a grid (which does not have to look like what I used! I just searched for a grid of the alphabet and picked one) or a circle (the same applies), a line is drawn successively to each letter:
http://i64.tinypic.com/ioq9e0.jpg
Some people might lay the ring sigil into a table of astrology, with the first letter upon that which best corresponds with the spirit in question, for example. The result may or may not be in a circle, and if a double-ring is used, it is often lined with significant characters or words, or just the spirit's name, or holy names, and the like, according to traditions. Again, WayTamer's post falls heavily into this, as many times additional content was found through different methods of divination.
As for the several posts in this thread who are just advising about how to create a sigil in general, this method may also apply. It creates an abstract image related to the statement of intent. It is one additional of the very many valid methods of sigil creation.
