Titanium is fairly hard, though not as hard as some hardened steel alloys it is quite a bit harder than brass. I would think you can use anything that you would use on steel, but try it out on a hidden spot first (since you are cleaning under the grips this should not be a problem). Titanium also polishes well too, so you can polish up any scratches if you do make some.
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"Among the many misdeeds of British rule in India, history will look upon the Act depriving a whole nation of arms as the blackest."
- Mohandas Gandhi, an Autobiography, page 446.