People use difficult signatures to make them look significant. Some people use their full names in their normal handwriting which doesn't show much of their personality.
Difficult signatures are developed so that they would be very difficult to be immitated. Most people go with complicated signatures so that they wouldn't be imitated.
People often choose the signatures that they know they can remember.
Some signatures are more meaningful to the person. For examples, some lines tend to have meanings to the person when they are from the right to the left or the left to the write.
Some people use complex signatures so that no one would be able to write cheques in their names.
People who use difficult or complicated signatures try to make them look fancy and pretty.
Signatures are very personal to the person because they train on it and take their time to develop it.
Some people have multiple signatures; especially famous people who sign autographs and bilingual people.