Interesting, in that there are two patent dates: Mar.14.82 and Aug.12.84. As invent4hir suggested, both were filed by E.F. Pflueger (note spelling) of Akron Ohio.
Patent 254,841 (granted 14th March 1882) was for “coating some surface of the harness, preferably a part of the bridle, or a thin metallic plate or other similar surface adapted to be attached to the bridle or harness, with a substance that shall be luminous the dark”.
Patent 303,318 (granted 12th August 1884) was for the attachment itself, including a claimed feature that it “shall be plainly visible at night”:
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From 1861 onwards (until recent times) US patent terms were usually 17 years from date of issue, so your rosette isn’t later than about 1899… otherwise it would have a later date for renewal of the first patent.