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|
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.