He's looking for this:
http://www.coppercoins.com/lincoln/...ie_state=ldsHaving found a few dozen of these over the years, I guess I'm qualified to speak here...
This particular RPM, while elusive, has a couple of definite indicators that you're looking in the right place. First, the primary mintmark is very close to the 95 of the date. If you're looking for this particular RPM, you can separate out the coins with a very high D mintmark and you will have at least sorted out all your candidate coins. Second thing is that the tail of the 9 of the date always appears to be lower in relief than normal - like there was some obstruction keeping the tail from striking up all the way. Just two observances I've made over the years.
The secondary mintmark is a little more "obvious" that many make it out to be. It's not a minute shadow that is hard to see even under perfect lighting. Actually the secondary D should pop right out at 5X, and is even visible to the naked eye under optimal lighting conditions.