You asked what to watch out for - and that depends on your purpose for buying them. If you plan to resell as the price goes up, you want to make sure you are buying from reliable brands and sources. Silver bars are hard to sell, so try an experiment: visit a coin show or coin dealer and ask how much they are paying today for silver ounces. That will tell you the gap you have to overcome to make this financially profitable. If they are paying $14 when silver is $18.50, silver will have to rise to $25 or $26 before they will even buy back at $18.50 + the premium you paid.

If you are one of those who thinks silver will become the currency in the event of a failure of the economy, consider whether a 1-ounce bar from a private mint will have more confidence than a 1-ounce coin that was issued by a government mint. (also, how do you make change for a 1-ounce bar? - at least with silver coins there are smaller denominations)