Yes, your handwriting does say something about you

Your signature, to be precise. A research study published in PLOS One studied how the size of the signature varied depending on how research subjects felt about themselves, even if they were not aware of it.

Dr Adhip Rawal, a lecturer in developmental psychology at the University of Sussex, School of Psychology in the UK, was the principal researcher who looked at whether the way people think about themselves would be reflected in signature size.

AIA campaign involving a face consisting of signatures

In one experiment, university students who were shown a positive word for 16 ms in a word recognition task signed their names 13% larger than they had on a psychological test taken before the task. There was a 0.8% increase in signature size if they had not seen the positive word. This effect was independent of what they reported as their mood at the time, and none of them reported seeing the positive word which had been flashed in front of them for just 16 ms, a time that had been previously shown to be beneath conscious awareness. 

While the research does not address this, the implications could be that customers, partners and colleagues whose handwriting is larger than normal might be more receptive to negotiations in your favour. And, that positive words flashed subliminally in presentations do have an effect on mood, even if viewers are unaware of them and if asked, would report no mood changes.

The challenge would be to get samples of signatures as a baseline. With everything electronic these days, handwriting has become as rare as hen's teeth.