PHP, 39 38 bytes

##no comparison operators

<?=($n=$argv[1])&PHP_INT_MIN?-1:1-!$n;

should work on most systems.

PHP_INT_MIN has only one bit set: the most significant one. If this is set in the input, it is negative.
!$n (cast to integer by the subtraction) evaluates to 0 for positive values and 1 for 0.

lame solution, 30 bytes

<?=($n=$argv[1])?abs($n)/$n:0;

works also on floats.

PHP, 39 38 bytes

no comparison operators

<?=($n=$argv[1])&PHP_INT_MIN?-1:1-!$n;

should work on most systems.

PHP_INT_MIN has only one bit set: the most significant one. If this is set in the input, it is negative.
!$n (cast to integer by the subtraction) evaluates to 0 for positive values and 1 for 0.

lame solution, 30 bytes

<?=($n=$argv[1])?abs($n)/$n:0;

works also on floats.

PHP, no comparison operators, 39 38 bytes

<?=($n=$argv[1])&PHP_INT_MIN?-1:1-!$n;

should work on most systems.

PHP_INT_MIN has only one bit set: the most significant one. If this is set in the input, it is negative.
!$n (cast to integer by the substraction) evaluates to 0 for positive values and 1 for 0.

PHP, 39 38 bytes

##no comparison operators

<?=($n=$argv[1])&PHP_INT_MIN?-1:1-!$n;

should work on most systems.

PHP_INT_MIN has only one bit set: the most significant one. If this is set in the input, it is negative.
!$n (cast to integer by the subtraction) evaluates to 0 for positive values and 1 for 0.

lame solution, 30 bytes

<?=($n=$argv[1])?abs($n)/$n:0;

works also on floats.

PHP, 39 38 bytes

<?=($n=$argv[1])&PHP_INT_MIN?-1:1-!$n;

Not using comparison operators. Should work on most systems.

PHP_INT_MIN has only one bit set: the most significant one. If this is set in the input, the input is negative. !$n casts to integer, evaluates to 0 for positive values and 1 for 0.

PHP, no comparison operators, 39 38 bytes

<?=($n=$argv[1])&PHP_INT_MIN?-1:1-!$n;

should work on most systems.

PHP_INT_MIN has only one bit set: the most significant one. If this is set in the input, it is negative. 
!$n (cast to integer by the substraction) evaluates to 0 for positive values and 1 for 0.