In the Standard GUI you can create symbols with arrows over them. Open the Layout palette, insert the Symbol with the `b' over the `A', then open the Arrows palette and change the `b' to the desired arrow shape. If you use lprint to print the Maple output, you can see how to create this via typing. The code inserted by the palettes contains optional fields to set the colors. If you are happy with the defaults you can omit them and then do, for example:

xvec := `#mover(mi("x"),mo("→"))`;

That displays xvec as an x with a right pointing arrow on top. Now, if you actually want to assign a Vector to the fancy x, things get a little tricker. Messing with the palettes gets tedius, so, you could set an alias (see ?alias for details). Using worksheet mode in the Standard GUI you could do

restart:
alias(`#mover(mi("x"),mo("&→"))` = xvec):

If you then type

xvec := <1,2,3,4>;

an assignment is displayed with the left side being the x with the arrow over it, the right side being the Vector. This can also be done in Document mode, but because the left side of assignments are normally suppressed, the x with an → over it is not shown, so there isn't much point.

To simplify the process you can assign a procedure

MakeVector := x ->  nprintf("#mover(mi(\"%A\"),mo(\"→\"))", x):

then use it as

alias(MakeVector(x) = xvec, MakeVector(y) = yvec):
xvec := <1,2,3>;
yvec := <4,5,6>;