It is impossible to make a personality assessment on a signature alone because it represents and reveals just one side of a person.
Your signature is your trademark, it is the face you show the world. It reveals how you want to be seen by others. The real you can be found in the main body of writing. You will have developed and practiced your signature over the years until it felt right. Even though it may appear the same to the naked eye, here will be little differences, either in the size, width or height.
Signatures can be legible or illegible, expansive or retracted, large or small, showy or neat. Many individuals have a couple of signatures for different purposes, for example one for professional or business and another for personal or private correspondence. Newly married women may find it difficult adjusting to her new identity and in the early years it is not uncommon for her to write her first name larger than her new surname.
Size (when compared to the main body of writing).
Bigger signatures reflect someone who has invested a great deal of themselves in their public image. The writer will want others to see them as confident and self-assured (though this may not be the case).
If the signature is considerably larger it suggests over-confidence or pretentiousness. A strong ego may be evident in an exaggerated signature but it could be a mask for inner self-doubt.
Smaller signatures suggest modesty or an underestimation of abilities, someone who does not seek the limelight. However, this interpretation depends on the rest of the writing it could be deliberately fashioned in order to gain advantage!
When the signature is congruent in slant style and size to the rest of the writing there is little pretence or veneer – what you see is what you get.
Writers who have to sign their name many times a day often resort to something akin to a hieroglyph for efficiency which, incidentally, is easier to forge. However, it can also express a lack of interest or desire to communicate clearly. Illegibility suggests an inordinate desire for self-protection and it will take time and effort to get to know the real signatory, or as much as they are prepared to reveal.