In the “Fudge” gaming system, one commonly rolls four dice, each numbered with “+”, “-”, and “0”. Since those are d3, and 2d3 are equivalent to a d9, you can emulate a Fudge roll with two of these dice (each one substituting for 2d3) without changing the odds.
I'm not sure about the numbering for this die. Using “++” and “--” didn't look so good for the double-plus/minus points, but “+1”/“-1” didn't look so good on the single-plus/minus spots. So there's sort of a hybrid notation here: one face reads “+2”, and one reads “-2”, then there are two labeled “+” and two labeled “-”, and then three labeled “0”, in order to emulate the odds of 2dF properly. The single “+” and “-” signs are designed to look different from one another even in bad printing.
The die is hollow, for minimal volume and smaller rotational inertia, and also has thinner curved sections than my other d9s, so hopefully should not roll too long.