ill give you a few letters that i think arent easily identifiable (to me), as i would have made them (NBPMH, there are two M's in the image i made) the main problem is that at 4x3, N's are real tough. i make em just like a lowercase but larger. if you did change to 4x4 it would alleviate this but i think that big 'n' is fine. i really couldnt tell what it was saying until i read below, i would defenitely change it either way. other than that, i think the P looks a bit like an F, the B looks like a blob, and M/H are too similar. the two things in the middle just dont look well for an H, and the single line for the M looks too much like an H. for H i would take out the top pixl and for m i would add another either at the top or right below the one you have. the M is the least of your worries though. also for reference i do two bottom pixels for a W if you thought my H looks like your W (you didnt show it)