Just like Silver coins, there are plenty of Silver bars to choose from. It is best to purchase the bars that are highly recognized in the US and abroad. When the Silver price eventually breaks over the $50 level, the amount of counterfeit coins and bars will make their way onto the marketplace. Some of the high end counterfeits will be sophisticated enough to be passed on several times. The internal will be some type of junk metal that will most likely be plated with Silver.
When purchasing bars, I like to stay with 1, 5 and 10 ounce bars. The reason is because you can sell fractions when you want. If you purchase a 100 ounce or 1000 ounce comex bars, you must sell the whole bar. This is fine for higher net worth individuals, but for most people, the lower demonetization will be fine.
Another issue to consider is if and when the government starts taxing on transactions over $600. You can currently buy and sell precious metals on ebay with no taxes. If the government initiates a tax on all transactions over $600, all of the bars over 20 ounces (at $35 Silver) will be taxable. When you have 1, 5 and 10 ounce bars, you will be able to sell in pieces without the tax penalty.
What bars to get? Two of the oldest minted bars are Johnson Matthey and Engelhards. They come in various sizes all the way up to 1000 ounce bars that trade on the Comex exchange. Most mints and countries produce their own 1 ounce bars for public investment, but they may be harder to sell when people cannot verify that is is 100% Silver.
How to tell if it is 100% Silver? There are small digital scales that can be purchased fairly cheaply through Amazon. Weigh the bar that you currently have and it should be exactly 1 ounce (or whatever size/weight). When you purchase the same exact bar, let say a Engelhard 1 ounce bar, it should not only weight exactly 1 ounce, but the size should be exactly the same. All metals and materials have certain weights according to the periodic table of the elements. If the size is exactly the same, but it weights more or less, it's a counterfeit bar.