If you do not intend on dropping the revolver much - - - don't worry about the hammer block. The way to tell without taking the gun apart, pull the hammer to full cock and look at the right side of the hammer slot. If it has a hammer block safety, it would be visible. Look at the first image in the link below to see the hammer block and the last image showing one without the block. If there is no 1914 patent on your revolver barrel, it should not have the hammer block safety. The hammer block was introduced around 57,500 serial number.
http://smith-wessonforum.com/members...-pictures.html
This safety device is not to be confused with a gun safety that will prevent one from pulling the trigger and requires an action to put it on and off. A hammer block type of safety that is a passive safety feature that prevents accidental discharge if dropped on hammer.