Moustaches were definitely a mandatory requirement for the army until 1916 - and I think the same applies to marines.
One possibility is that the last letter is actually an R rather than an A. This could give us RFR for "Royal Fleet Reserve", which would actually make sense for RMLI.
As far as I know, these white inscriptions were written in reverse on the negative before the photo was printed, so I suppose that could explain why the big 'R' is in the middle - I have seen similar errors on photos before.
However, I'm not totally convinced - just an idea!
T