[Bigdaddy]

I think the earlier signatures are generally more sought after, but more so because they are easier to date and represent an earlier time in their career (sort of like rookie cards).

There are some players who have stark contrasts in their signatures due to strokes or other physical incidents that have a distinct 'before/after' rather than the gradual changes due to age. Two that immediately come to mind are Carl Hubbell and Buck Leonard, both of who had strokes later in life but kept signing autographs.

For more recent players, many times their signature changes (usually in the direction of looking more like a scribble) due to the fact that they become more popular and the demand for their signature increases.

Probably the most recent example of completely changed signatures is Randy Johnson (Big Unit). He has two or more distinct styles of signatures that in no way resemble each other.