fret markers.
General mountain dulcimer or music discussions
@jp, I have two comments here which are kind of contradictory. The first is why you should not need fret markers. The second is what to do if you get them.
First, to get used to the 1-1/2 fret does take some time. It took me about a year even though I'm used to chromatic instruments such as the guitar and mandolin. When I finally "got" it, it was just a matter of mental focus. I forced myself to think "fat, fat, skinny" as the beginning of the fretboard. The first two frets are fat, then comes that skinny third fret. Once I started imagining the space on the fretboard as indicating where the notes were rather than the fretwire itself, I stopped getting confused by the 1-1/2 fret. If you put fret markers in those normal places (3, 5, 7, 10), which I strongly suggest so that you don't get confused by other dulcimers with fret markers, they will not necessarily help you get used to to the 1-1/2 fret. That's just a hurdle you have to overcome.
Second, I agree with you about what kind of markers to get. If you want something temporary, just use masking tape. If you want something that you plan to leave on for a while, get nice inlay stickers. The ones I got are easily removable and don't leave any trace that can't be wiped away easily. They are also so thin that you don't notice them at all when fingering the fretboard. Until you look closely, they appear to by nice inlay, and you can choose a variety of different designs, so you can personalize your instrument pretty easily. Be aware that most are made for guitars, which usually have a wider fretboard than dulcimers do. And if the fret markers involve a design that connects several frets in a row, they won't work on the diatonic fretboard of the dulcimer. I think the ones I got were made for a ukulele, so they're pretty small. The website I linked to earlier has a range of shapes, sizes, colors, and designs, so take your time looking through the options and find something that will not detract from the look of your dulcimer.

, but the music plays on.
Jeepers, creepers, you gotta protect your peepers!
got me a $100 gift card to Just Strings for my last birthday. I was able to buy several years worth of strings with that.
You are going to get tons of advice from this site, and some of it might even be helpful!