Is there a standard way of distinguishing between scalars and vectors in handwritten notes? In printed math texts, one can distinguish between scalar variable and vector variables because the vectors are in boldface. However, that doesn't seem to work as well when I take notes by hand. Is there an alternative standard for denoting vectors that is more suitable for handwritten notes? I find that I sometimes have trouble distinguishing between scalars and vectors in my handwritten notes, as it's not always clear from the context.
 A: I just use different letters for them: typically $u, v, w$ for vectors and something like $x, y$, or $c$ for scalars. If there are a bunch I'll use subscripts, e.g. $v_i$ for a bunch of vectors and $c_i$ for a bunch of scalars. 
A: I think many notations exist for a vector. Since I was undergraduate student, I use upper small arrow to indicate a vector, like this $\vec{v}$. In Japan, people use 'artificial white bold' letter, similar to this $\mathbb{V}$ (but small case, as if you want to write the notion for real number ($\mathbb{R}$)). I prefer using upper small arrow though.
A: Underlining a letter to denote a vector quantity $\underline{v}$ is common practice and easier to write than arrows, and the text looks less cluttered. 
Matrices are double-underlined $\underline{\underline{M}}$ when hand-written to distinguish them from vectors and from scalars which have no underline and are frequently Greek letters.
For example, you can write the eigenvector equation as:
$$\underline{\underline{M}}\underline{v}=\lambda\underline{v}$$
[Someone who knows Mathjax better will be able to edit my double-underline to make it look neater.]
