Additional Markers for Standard Marking System
Dan Landrum has devised a method which helps him navigate on the LC. Pictured is a 12/14/13 LC. Red marks the Gs, Blue marks the Cs and Green indicateds the Ds. He printed out the colors on his color printer, punched them out using a hole punch and then with a razor cut them in two and stuck them under the neccessary courses with a touch of glue applied with a toothpick. Very low tech! He is playing an LC marked with Standard Marking but you could devise something similar to augment the Piano Marking as well.
The little colored and white pom poms are installed to deaden sympathetic vibrations in tails of courses that are just sitting there waiting to produce some extraneous noise. Bass bridge close up. You can see them to the right of the rod. The pom poms shown in this photo aren't as necessary for eliminating rattles as the ones on the right side of the aluminum rail (see top photo). They do help keep the overtones down though. Since the pom poms come in primary colors Dan makes them match the bridge markings of red, blue and green. Where there is no color marking he has them match the rod. He uses yellow for the brass.

The following is Dan's rationale for the additional colored marking of the Standard Marking System

While the linear chromatic may appear to be a little harder to understand for those unfamiliar with the extra notes, it is actually easier to grasp theoretically because of its consistency. For example: When showing someone the standard diatonic layout, or even worse the diatonic with added chromatics layout, you must teach them about as many exceptions as rules. "This note on the left side of the bridge is the same as the one on the on the right side and up five strings - except for when you get to here, then there's a half step difference, but here the pattern begins again . . ." On the linear chromatic all the notes repeat and you can quickly play any interval by just changing the separation of your hammers. You are moving in half-steps so to go from a major third to a minor third you just bring the hammer playing the third one string closer to the root. True music theory is very easy to see and teach on the linear chromatic because all the notes are there. The added notes however make for less vertical note range in similar sized instruments. James has solved this problem by adding another bridge to the left of the standard treble bridge. Almost everyone I've demonstrated this to has been surprised to learn that you can play on both sides of this bridge giving you incredible range in a small box. This also creates the option for playing many patterns horizontally as well as vertically. It was this added left hand 'super-treble' bridge that I had the hardest time "seeing" at first. I could quickly see the diatonic markings but because I wasn't used to it being there, I wasn't sure at which course I was looking. That is when I came up with the idea for the color markings. I wouldn't think of playing a harp without the standard color markings so I thought I'd give it a try. It was amazing. My confidence level jumped dramatically when I didn't have to think so much about where I was on the instrument. The system is similar to that of a harp which uses red for C, and Blue or black for F. Another way of looking at it is Red for the root note of a I chord and blue or black for the root note of a IV chord. Harps are C-centric instruments but my linear is a G-centric instrument so my markings are:

G - Red
C - Blue
D - Green

As you can see in the photos I just put little half dots underneath the string with rubber cement. They come off easily without leaving residue as I discovered in the multiple color schemes I tried before settling on this one. I won't be taking them off though. The instrument is just so much easier to read now. I also discovered that it is much easier to teach new students with this marking system. For instance, take someone, perhaps a child, and show them where the G is on a standard diatonic instrument. Now explain the concept of how a G# is one half step higher and a Gb is one half step lower. Next ask them to identify all the G#'s on the instrument. It is easy to see even on a piano because of the repeating patterns. But since the patterns only partially repeat on a diatonic hammer dulcimer it is a really tough exercise. And even with the consistent repeating patterns on the linear it is difficult without the markings because the patterns are scattered across different bridges rather than being spread out in a line like on a piano. Put the marks on and red is instantly recognizable as G anywhere it appears. Go up a half step and you're playing G#. It is that simple. I've met many seasoned players that have to stop and think about where the Eb's are on their diatonic instruments. On the linear it is right above the D which is green and easy to find.