How to get sign of a number?

In PHP 7 you should use the combined comparison operator (<=>):

$sign = $i <=> 0;

A variant to the above in my question I tested and which works as well and has not the floating point problem:

min(1, max(-1, $number))

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Edit: The code above has a flaw for float numbers (question was about integer numbers) in the range greater than -1 and smaller than 1 which can be fixed with the following shorty:

min(1, max(-1, $number == 0 ? 0 : $number * INF))

That one still has a flaw for the float NAN making it return -1 always. That might not be correct. Instead one might want to return 0 as well:

min(1, max(-1, (is_nan($number) or $number == 0) ? 0 : $number * INF))

You can nest ternary operators:

echo $number, ': ',  ($number >= 0 ? ($number == 0 ? 0 : 1) : -1 )

This has no problem with floating point precision and avoids an floating point division.

Here's a cool one-liner that will do it for you efficiently and reliably:

function sign($n) {
    return ($n > 0) - ($n < 0);
}