I prefer there be no effect.

with an effect you will know that it's someone who has the item, and more nades... and that there will most likely be more of them coming your way soon... it's also generally the classes that have abilities on nades who purchase the item... so if you see some form of effect, you'll know 2 stay back and play it safe... I like the concept of people fearing nades all the times as they wont know if it's just a standard nade, or one that most likely has a ability on it 2 boot.