Delokaver,
You don't need the triac at all anymore. The modification suggested by Ubergeek completely eliminates it. See the schematic attached to my previous post. If you are planning on building this thing, I would highly encourage you prototype it first to ensure it works as expected. I didn't actually test any of this. The value of R2 will set the off time or time in between pulses. The value of R3, R4 and R5 will set the on time or the time the led is lit. R3 and R5 should be equal value and R4 should be a higher value than them to make the middle three pulses longer. Another improvement could be made if you join the wires coming out of D2 and D4 before the resistor, you can use a single resistor in place of R3 and R5. That way both of the ... portions of the SOS signal will be equal and not slighlty different due to individual variations in resistor values. Whether or not that would be noticable is questionabe.