How about a question box when you attempt to pick up a No Drop item? "This item is classed: NO DROP. You will not be able to trade, sell or drop this item should you collect it. Are you sure?". Or something like that anyway. I've accidentally picked up a no drop item twice now, and while that isn't much, it means two people lost out on something that could have been useful for them. It makes me feel bad, and probably annoys them.
Maybe have it only while grouped? Though personally I'd like to see it all the time. What do you think?
Spookdoc/Majikall - Rubi-Ka 2