Yup, thread locking compound. Vibration has a habit of loosening nuts and bolts. Nylon lined nuts were made to combat this (and are very effective at it, but can't be used in all situations) Loc-tite works on the same premise that Nylon does. Almost like a glue, or rather could probably say it IS a glue, just a very weak one as far as glues go.
One thing, I ride with 3 different CBR929 riders. ALL 3 have had bolts mounting their tale subframe to the frame come out. One of them lost THREE bolts over this past summer. All 3 have since used loc-tite on ALL their subframe and frame bolts on their bikes.