[CurlyDave]

...It's an interesting hypothesis but it seems that too many stars are emitting these signals. That would suppose a huge civilization...

This is not necessarily true.

Numerous civilizations all doing similar things would produce the same observation.

This does not even require invention of the same technique by numerous groups. One species sends a signal another one sees it and says: "hey, we can do that too..."

Or a civilization achieves travel to a nearby star and sends a signal from there -- much smarter than putting up a billboard that says: "come and get us."

[UCANSEE2]

Numerous civilizations all doing similar things would produce the same observation.

OK. Let's say we want to send a signal. Can we produce this same signal ?