It is hard to tell from the photo, but if it is more scab-y (which it look like to me) than dried, stuck-on crusty stuff, I would say it is probably vent disease. Rabbits can get it on their face whether or not there are any signs on the genitalia. You can do a google search to find the appropriate dosage for Pen-G, which is what we usually use for vent.
If it is dried, crusty nasal discharge, then it could be any number of respiratory infections or irritations. It could be something as innocuous as a piece of hay or pellet stuck in the nose to something as dreadful as pasturella. Some people cull immediately for nasal discharge while others will quarantine and watch. Some will treat depending on the cause. Pasturella cannot be cured, only symptoms controlled. A culture is the best way to know if you are indeed dealing with pasturella.
It does look more like vent disease to me, though.