Sniper lore is full of instances in which "glint" gives away position--with adverse results to the reflecting party. Top Soviet sniper Vasili Zaitsev killed Germany's legendary Maj. Koning by spotting and targeting a reflection from Koning's scope after a three-day duel during the Battle of Stalingrad. Israeli Gen. Moshe Dayan wears an eyepatch due to an injury sustained when an enemy sniper shot at the reflection from his binoculars. Our own famous Marine sniper, Carlos Hathcock, shot an opposing Vietnamese sniper right through the scope tube by firing at the glint of the enemy sniper's objective lens. It's a good thing Hathcock was fast on the trigger, but it makes you wonder what would have happened if the Vietnamese had had an Anti-Reflection Device on his scope.
A classic method of reducing reflection from an objective lens is by attaching a long sunshade. If long enough, the shade eliminates reflection unless the optic is pointed almost directly into the sun. The downside is bulk and slightly reduced light-gathering ability.
More effective is a honeycomb-type ARD such as the ones produced by Tenebraex Corp. The geometry of a large number of tiny tubes in a honeycomb pattern reduces the length-to-with ratio necessary to eliminate glint, allowing the device to be effective at much shorter lengths. There is some light reduction--in the neighborhood of 15 percent--but resolution is basically unaffected. The unit simply screws into the threads in front of your optic's objective lens. Contrary to what one might think at first glance, no shadowing or distortion occurs. From the ocular end of the optic, you can't even tell the shade is attached.
Models are available for selected Leupold, Nightforce, and Schmidt & Bender scopes as well as several Trijicon ACOGs and the M68 Aimpoint. Prices range from about $50 up to $95.