Alistair Reynolds has it here. Thankfully it wasn't coded in undecryptable French or somesuch.

Sample...

The next step, should you choose to take it, is to participate in the Galactic Information Network by replying to this message! It's easy - all you have to do is generate a modulated gravity wave signal with a source strength of around four billion billion Megawatts! That may sound a lot, but it isn't really - it's only one percent of the energy output of the G-type star your planet orbits! Go on - you won't miss it!

Also, please don't reply to any transmissions originating from the M13 globular cluster in Hercules - and never, ever send them unsolicited messages! Especially not radio - they hate radio! Also beware of messages claiming to originate from ascended level 3 cultures, especially those which offer suspiciously cheap Dyson conversions of your solar system! Believe us - they are too good to be true! You'll also want to keep away from any entities posing as the legal heirs of the capital assets of the fallen level 2 culture on the edge of the Cygnus Loop - and you definitely don't want to give them the coordinates of your system!

PS - When appending content to incoming messages, please do not top-post.

**************

P.S. No Lindy - this is NOT real. Trust me!