In the United States, there are signage on or near existing 4G or 4G LTE transmitters, it looks like this:
An actual (stock) photo example: https://c8.alamy.com/comp/B6P4B3/a-sign-warning-about-radio-frequency-fields-B6P4B3.jpg
The statue that the sign claims to be in compliance with is this, but as with all law-speak, I can't really see where it says a sign is required. https://www.law.cornell.edu/cfr/text/47/1.1307
Addtionally, here is the section with technical details regarding Maximum Permissible Exposure: https://www.law.cornell.edu/cfr/text/47/1.1310
Safe distance isn't determined by any specific number, or general guideline. It wholly depends on the equipment, the power, etc. So the distances can vary greatly. I found a slide from a presentation that breaks down one company's approach to the different measurements and which type of signage to post.
But these values only really exist within the same height of the transmitter. If you want a visualization of the general un-safe area, look up Fresnel Zone. As long as this area does not overlap with places where people are, there shouldn't be any issues in regards to health due to to the power in the air. The system is not designed to transmit to the ground, only through the air. As such, it is expected that even directly below the transmitter, any measured readings should be well within the safe zone, same as existing 4G and older setups. So the telecom company would only be able to put transmitters above houses. In my neighborhood, they would be fine to put them on the TOP of telephone poles because the heigh of a telephone poll is taller than the houses on my street. There are no three story or taller buildings. However, if they are placed somewhere between the top and say... the middle, this would put the 2nd floors of almost every house in the neighborhood into the broadcast zone and then that would be a real problem. I have seen some research on existing consumer 5G transmitters, and it seems there is around a 100 yard (300 foot, idk about meters) distance from the broadcast point in line of site to fall below that 20% example shown in the slide above. Of course, consumer transmitters and the ones used by telecoms may be totally different.
More reading on this subject in general: http://hps.org/publicinformation/ate/faqs/cellphoneqa.html