You also don't want to annoy/distract people, our hobby will be under growing attack as what's easily available to the public becomes stronger and as morons intentionally use lasers to harass or accidentally harm people, freedom requires personal responsibility, be safe and respectful or we will face new legislation to restrict our fun.
If beaming unmanned communications towers is not illegal it will be if it's provoking a response, but I wouldn't think projecting a harmless dot on the wide shank of the tower or onto a water tower would be illegal, but if that tower is visible to cars on a roadway then you could be distracting people and we all need to STOP, LOOK and LISTEN before lasing outdoors, make certain there's not a maintenance worker on that tower before you beam a harmless spot onto it and stop doing whatever it is if you provoke a response, that's just common sense, don't think just because something isn't yet illegal that you should abuse it, that's how you screw up the fun for everyone.