Is there a difference in handwritten nabla $\vec{\nabla}$ with an overset arrow and typeset nabla $\nabla$? According to some physicist at KIT it is usual to write the following when using pen and paper:

whereas in typeset texts you write $\nabla$.
Is that true? Are there sources for this convention?
 A: *

*Yes, there are sometime different conventions for indicating vectors in hand-writing and printing. 

*Yes, overset arrows in handwriting and boldface in printing is one of those conventions. 

*No, it is not the only convention.

*Yes, you should familiarize yourself with the most common conventions in your sub-discipline.

*Yes, you should read the section on notation in the introduction to each book before proceeding. (And if writing a book you should write a section on notation.)

*Yes, is get more complicated still if you want to visually distinguish more than just two types of values (say scalars, three-vectors and four-vectors).
A: Yes, the reason for this is that in maths $\nabla$ is often used as the vector differential opertator. This is a vector. When typesetting the convention to denote a vector is bold text e.g. $\bf{x}$. However for handwriting you can't really write bold font so other conventions are needed. Common ones are putting an arrow over as in your example or underscoring.
Note this is probably not how this notation was developed what with handwritten maths having existed before typesetting but this is the standard modern useage, although some books using other typesetting.
