Welcome to the forum. Yes, it certainly can all be very confusing at the start, I'll try to clear some of it up.
We are talking about American silver here, so the first thing to clarify is that there is no such thing as a hallmark on American silver. To have a hallmark, the silver must be made under one of the British or Continental systems where there were governing bodies or trade organizations called guilds that had guild halls, hence hallmark. In America, marks on silver are maker's marks, trademarks or manufacturer's marks.
The predominant American standards used on solid silverware were Coin (.900, roughly pre-1870) and Sterling (.925, roughly post-1870). It is important to keep in mind that solid silver wares always were, and still are, luxury goods for which people have always paid a premium. Given that, it has always made sense for the maker to clearly label the item with something indicative of its luxury status. This is why 99.9% (the figure is a guess, but I'm confident that it is not far off) of all American solid silver made after 1870 is clearly stamped "Sterling" or in more recent years .925, just plain stupid for a maker not to choose to do this. If a U. S. piece made after 1870 is not stamped "Sterling", it is almost always plate.
In the 18th & earlier part of the 19th century, silverplate had not yet made an impact on the market so there was no strong need to differentiate between the two types of ware. American pieces of this time are often stamped solely with a maker's mark. But, as silverplate became more prevalent and the later the year, the more common it became for makers to stamp an indicator mark to show that the piece was solid silver. Some coin silver indicator stamps are; "Coin", "Standard", "Premium" and the letters "C", "D", or "S" found amongst coin silver pseudomarks are also thought to be indicators.
You'll notice that the silver marks and silverplate marks are in separate sections on the site. In the American Silver section, you can safely assume that the marks found are stamped in conjunction with some sort of silver standard indicator mark, unless they are early coin silver smiths.
There are American manufacturers that produce both silverplate and sterling, generally speaking, they tended to use different trademarks on each type of ware, however, there are some that did use the same trademark on both sterling & plate, but you can rely on the fact that the sterling items will be stamped as such. There are also many silverplate manufacturers that use marks that are imitative of older British and Continental hallmarks. Familiarizing yourself with genuine hallmarks will eventually show you just how cheesy these copycat marks are.
All that said, and despite having set up a website devoted completely to silver marks, I need to point out that one should not rely entirely on the marks. There are many other important indicators as to; silver or plate, antique or recent, handmade or manufactured, treasure or trash - and that knowledge is acquired through the handling of many, many pieces of both silver and silverplate at shops, shows, auction previews and where ever else you can, literally, lay your hands on it.
Hope this helps.