Why PHP's float 0 (zero) is being displayed with sign?

In PHP, lets create a variable and set it value to 0:

$x = 0;
echo $x;

it would display 0. If one would multiply that by -1:

$x = -1 * $x;
echo $x;

we still see 0. But if $x is a float:

$x = 0;
$x = (float)$x;
$x = -1 * $x;
echo $x;

we would get the output: -0.

Why is that? Shouldn't zero be always displayed unsigned, regardless of its underlying type?