The distinguishing cuts made into an animal’s ear are its earmarks. They work like brands to mark ownership. Originally gold and silver articles assayed at Goldsmith’s Hall in London received a “Hall-Mark” to certify them as genuine. In modern usage “earmarks” and “hallmark” are used in many other contexts and mean pretty much the same thing, except that we say “it has all the earmarks” of someone or something, and a certain characteristic is “the hallmark” of someone or something. Although a great many people pluralize this expression too, traditionally an item can have only one hallmark.
We speak today of parts of bills being earmarked when legislators set aside certain expenditures in them for particular purposes which benefit the legislators’ own constituency. They lay claim to public resources just as a shepherd would earmark a sheep to lay claim to it. Note that no one hallmarks a bill. If we said a bill bore Senator Blowhard’s hallmark, we would mean that it bore some characteristic pattern by which we could recognize his influence on it.