Wow I just had this issue, and my whole rear wiring harness was chafed through the rear hole in the fender causing shorts and all kinds of problems. But that caused all the signals to flash rapid flash with any direction of a turn signal. Got all the wires affected all spliced and medic'd up. Back to working amazing, now!
What year is your RM? Does it have any incandescents on it? I'm guessing no, but I guess the first question is if everything is still stock. Fuses under the left side cover? I'd have to go out and look at mine, but I thought I found one there once. Or maybe it was my Honda before I forget.
Then check the connectors. May have to take off at least the headlight and center piece if you have the locomotive front. Or maybe the fairing if it's the other style (I don't know I have the locomotive style on my 19 RM). The turn signal connectors could be trapped behind the aux lights if they are fairing mounted and the whole front of the fairing would have to come off anyways. And if you have to replace a turn signal if it is the fairing mounted turn signal it would have to come off anyways to replace that if it is just the front left one.
There is a main plug under the seat to check also for the front to rear connectors in the wiring harness. Maybe some corrosion on a pin or something too some how in any part of a connector. Just something to check. Also for pinched wires.
How long have you had it and this is the first issue? Lots of just general stuff to check out. Here was my issue, lets hope it's not something like this for you, too. Hope something in all the blah blah helps out some how!