For spray your best option is going to a local hardware store and buying a satin black poly shake can, simmilar to that of a spray paint can. For a non spray satin finish, I recommend clear butchers wax (used on boling alleys), although this finish can be buffed to a high gloss under a normal amount of buffing it gives a very nice satin finish. Also keep in mind poly is very hard to repair as you have to take all of it off to repair a scratch (it does not scratch easily), and most poly yellows over time. Also make sure when you buy the spray black paint it is satin as well, or it will gloss up. My recommendation is to use butchers wax.
note when I say poly I mean polyurethane, which is bascially varthane, or most epoxy finishs. (which are poly urethane based)
For the finish above you may want to use semi gloss poly and then kill a little of the gloss with 0000 steel wool, as the finish above is not comletely satin but rather something of a semigloss.
(this as well could be acheived with a well buffed butchers wxax finish.