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It's a great question, but I bet that we beat any signal that we send out by developing faster signaling technologies.
I'd bet that we will pick up the Pioneer and Voyager craft and put them in a museum someday. If we have to use light then I would go with primes too. But, I don't think it matters what we say. The real message is that there is a message. Once they found it they'd start listening to all the junk that we leak into space, and building instruments to listen better.