I do not know whether the ISS has a strobelight attached, but I suspect not. Even if it did, such would be very difficult to see from a distance of several hundred kilometers as you viewed it. The brightness of a satellite is due primarily to its illumination by the sun -- this light is enormous compared to a small lamp or strobe. Satellite flashes are usually due to flat solar panels or the like catching glints of the sun and reflecting them like mirrors to distant observers. As many satellites spin, this could be the cause of the phenomenon you observed. It is also possible that you were witness to a high altitude plane with an unusual strobelight pattern. The mirrored ball released by the shuttle during its recent flight produces a continuously blinking appearance and not the patterned protocol you witnessed.