Indeed, within those 5 million years, we've produced coherent electromagnetic signals for just a bit over 100 years, and will probably go dark again before another 100 years elapse. Already, most of our electromagnetic information bandwidth is confined to fiber optic cables. Like a primitive Dyson sphere. Our remaining free space communications are increasingly designed to be virtually indistinguishable from noise.

Perhaps the evolving spectroscopic signature of our atmosphere will provide a durable signpost. The earth terraformed itself well before intelligent beings ever evolved, and maybe an astute and patient observer might have been able to guess that we were on our way towards intelligent life at some point.