What you need is throw, not necessarliy lumens - some HIDs might do it, not really sure what wattage and reflector is necessary to be visible at 10 miles, that's a question for the HID and incan forum.
What I would wonder, though, is a whether good strong laser would be visible, if you can aim it at the target microwave receiver accurately enough. I would think a 200 mw laser should be easily visible at 10 miles, if you are within the beam and visibility is clear. Probably only puts out about 100 - 200 lumens, but it is pure collimated photons. A green one should be easy to pick out from any other light sources.
But I am not an expert, and would have to test this to really know. Hard to find 10 mile line of sight testing sites to try my 100 mw green laser with, especially where I live - I would need at least 30 meter towers at each end, or some combination of relative heights above the ground equalling something like 60 meters. Of course this is why those microwave transmitters are always up high...