item  notation 

multiply product  cross sign, e.g.
a×b

matrix product  dot sign, e.g.
a⋅b

scalar product (product of a matrix by a scalar)  dot sign, scalar should precede matrix e.g.

matrix dimensioning 
number of rows × number of column, e.g.:
R×C

Kronecker product  a⊗b 
bracketing of sets (all elements of same type, not ordered elements) 
curly brackets {}, e.g.

bracketing of lists (all elements not necessary of same type, ordered elements) 
round brackets (), e.g.
(A, u, x)

bracketing of sequences (all elements of same type, ordered elements) 
angle brackets, e.g.

bracketing of function argument 
round brackets, e.g.
f(x)

bracketing of array index 
square brackets, e.g.
a[x]

bracketing of matrix or vector 
square brackets [], e.g.

Separation of indexes 
use a comma: e.g.
N_{i,j}

use of italic for symbols  a symbol should be either in italic or in normal font, but mixing up should be avoided. 
bracketing of arithmetic expression to force precedence of operations 
round brackets : e.g.

necessity of bracketing arithmetic expressions  When only + and × bracketing is not necessary. When the mod operator is used explicit bracketing of mod operands and possibly result should be done. 
number type  in a context of non negative integer numbers, some notes should stress when a number is signed, or possibly fractional. 
binary xor and and  respectively use + or ⋅. If no "mod 2" is explicitly in the expression some text should stress that the operation is modulo 2. 
matrix or vector transpose  v^{T} 
1x1 matrices  implicitly cast to its unique element. 
vector dot product  u^{T}⋅v for column vectors, and u⋅v^{T} for line vectors 
complex conjugate  v^{*} 
matrix or vector Hermitian transpose  v^{H} 
real part and imaginary part of complex numbers  Re(x) and Im(x) 
Modulo operation (including negative value) r ≡ a mod N 