Is there any scientific study on handwriting by profession? In the whole world, the people with the most control of their muscles are athletes. Or pianists, who have extremely good control of their fingers. So perhaps their handwriting will be different from the average person?
Short answer: Not really, because a) handwriting style is generally individual-dependent and not occupation-dependent, and b) the fine-motor skills responsible for handwriting legibility are specific enough to be near-independent of the muscle control that mandates one's success in athletics and/or music.
It is probably difficult to say anything definite about the variance in style of handwriting among profession, as handwriting style is something subjective. Furthermore, one's handwriting style is typically well-formed before the time of their occupation.
In terms of the objective nature of handwriting -- i.e. its legibility and general readability -- there tends to be a greater relationship with fine motor coordination. However, even then, the motor coordination is fairly specific to handwriting or letter generation. The ability to generate written text is largely dependent on orthographic-motor integration  and finger sequencing.  The latter variable may be practiced by musicians or certain athletes in specific sports, but these variables are by-and-large specific to handwriting and letter generation. In general, a greater indicator in how legible one's handwriting will be is how 'automatic' one's handwriting is. Thus, interventions that promote higher orthographic-motor integration tend to improve the 'automaticity' of one's handwriting, thus leading to better legibility and readability in their handwriting.  Again, these interventions are specific to handwriting, and general fine-motor skills typically do not affect this area.
You might also be interested to know that there is a field of study called graphology that attempts to analyze handwriting based on personality or personal characteristics, such as profession. However, it is largely regarded as a 'pseudoscientific' field due to its lack of reproducible research thus far. I mention this because a lot of the resources I found when looking up more information on this question came from books on graphology, and so I could not use them as scientific resources. :)
 Jones, Dian; Christensen, Carol A. (1999). Relationship between automaticity in handwriting and students' ability to generate written text. Journal of Educational Psychology, Vol 91(1), 44-49.
 Berninger, V.W.; B.J. Wolf (2009). Teaching students with dyslexia and dysgraphia: Lessons from teaching and science. Baltimore, Maryland: Paul H. Brooks Publishing Co. pp. 1–240.