personally i'd go with the less conventionnal :
if ($bar > 0) return "YES";
if ($bar == 0) return "MAYBE";
..somewhere between ternary and switch disposition, i find it clearer, obvious and fautless performance-wise.
The point of concern is when another dev replace the return with more operations defeating the "escape" purpose of "return" statement.
So i can understand that the "else" are somewhat preventing falling through.
However, as $bar cannot at the same time be 0 AND superior to 0 AND something else, i'd say it's safe.
In terms of control structure it calls for a switch, however many people reject this form :
case ($bar > 0): return "YES";
case ($bar == 0): return "MAYBE";
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