The round end of a small ball peen hammer is what I use. I also cut the pins just a hair longer than "flush" to mushroom them out. the round end makes a nice "dimpled" texture. The smaller the hammer, the smaller the "dimple". You can also make a "hand hammered" finish on brass bolsters or guards and subhilts using the same technique. I also put a piece of tooling leather or a piece of thick rubber gasket material between the piece I am "peening" and the anvil part of the vice so that it doesn't mar the finish on the underneath side from the impacts of the hammer.