Which adhesive sealant for bathroom fixture escutcheons?
I did mine with clear silicone.  Everything must be bone dry before application.  Just push the escutcheon flush to the wall and apply silicone around the outside where it meets the wall. The key to a good job with silicon is to make sure you don't over apply. Nothing is worse than having silicone spread out an inch past where it's supposed to be, especially on nice stone.  To prevent this, put some masking tape down first, both on the escutcheon and the wall.  It is hard to get tape to go around a circle, but the taping job doesn't have to be perfect. Leave a 3/16" gap for the silicone to adhere to the surface.  Apply the silicone and smooth with your finger.  For best results, dip your finger in mineral spirits (not water) before you smooth the silicone.  Make sure you pull the tape up before the silicone cures.