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I have never tried it, so I'll extrapolate.

If the criterion is "to be visible" to the target, then heck yes. A little keychain LED light for lighting up a door keyhole can be "seen" over a mile away on a dark night. I've done Morse sessions with the Scouts like that with a blue Photon II microlight. I have been camping in the mountains and I have seen a single porch light over a distance of several miles- probably a 60 watt incandescent that sprays out in a big circle, not concentrated and directional.

I've been in a commercial jet at altitude, 32-38,000 feet, and seen searchlight beams from below, those four-lights-on-a-truck kind.

I live near an airport and I can see the landing lights of the incoming birds a long, long way out. They turn them on out by Diamond Bar, CA, and you can see them snap on from Marina Del Rey. Those are only a hundred watt incandescents, I think, in a parabolic reflector, and the drive time is about an hour so maybe 40 miles?

So I think it would be safe to say that if you were up on a mountain, let's say near Big Bear Lake in California where you can get a good view to the East, and someone down on the Pearblossom Highway or in Landers beamed you with a 5 mW green laser pointer, you'd see it. You can see car headlights at that distance, about 10-12 miles, so something as bright and distinctive would stand out as a bright green spark. The beam diameter would be pretty big and the beam from a 5mW laser would not come close to damaging your eye. Earlier I calculated beam power at .46 microwatts/cm2 at a range of 10,000 feet, not very intense. You wouldn't see a heylookitthat bright beam sizzling through the air up on Big Brear but if you looked down at the beamer's location you'd see the laser.

The beamer would see the beam seem to reach from the laser all the way to your location, which is why astronomers are using them for pointers. That's a distance and perspective illusion, the scattered light from the beam gets dimmer with distance. I think but am not sure, that people close by would see the beam out to maybe a mile away, but further away they wouldn't since the scattered light would diffuse out quickly.

When Vegas used to allow laser sky shows, you'd see the beam when you were fifteen miles or so out if you were driving in, but those were up in the watt class not milliwatt. Now the big white light on Luxor can be seen for a good distance, it shines straight up, but they curtailed laser skyshows. Catching a one watt laser light show beam in the face while flying is orders of magnitude beyond the laser pointer (see my post about the FAA open-air laser regulations, it has a link to a report that has laser power/distance relationships).

Light does not stop until it hits something. When someone says that a flashlight, laser, or spotlight has a range of one mile, or 10,000 feet, or whatever, the light keeps going after that. The range is mostly a marketing ploy but usually means that's the distance at which you can tell when you hit something. So if you buy a red laser pointer, I got mine at Wal-Mart on sale for $12, and they say it has a 3000 foot range, they mean that you can see the laser spot after the coherent beam goes 3000 feet and the diffuse return reflection goes back to you another 3000 feet, getting weaker and more spread out all the way. If that's the case, then if the viewer is 6000 or more feet away, he'll see your laser as a bright light, but the light bouncing off his white van (say) is too diffuse and dim for you to see. You won't know it, but you tagged him!