This questions is probably similar to witch hexes and other mind-control spells, but seems different enough to ask.
Halflings with this racial trait gain the ability to curse another creature with bad luck at will as a standard action. This curse has a range of 30 feet, and you must be able to see the target and have line of effect to it. The target gets a Will saving throw to resist this jinx (DC = 10 + 1/2 your level + your Charisma modifier). If your target makes this saving throw, it is immune to your jinx ability for 24 hours. A jinxed creature takes a –1 penalty on all saving throws. This jinx lasts for 24 hours or until you attempt to use your jinx again. A jinx is a supernatural ability, is not mind-affecting, does not allow spell resistance, and can affect any kind of creature not immune to luck effects. This replaces halfling luck.
If my halfling targets someone with the jinx, does his enemy or other observers know they are being jinxed?