Lower income people (including a lot of renters) tend to smoke.

Maybe they meant smoke detectors, but CO detector. 

For those of you with multiplexes, do you use smoke detectors that are "linked" to each other? 

A part of me would speak "internal voice" why don't you go buy your own place where you can smoke inside (including weed), leave your space heaters unattended, have 20 plus smelly rabbits, bring in the homeless, pile up crap in the garage to where it is a no-walk or "walk at your own risk zone", drink and wake up every morning yelling and screaming at each other all while waking up the entire peaceful quiet cul de sac, change locks at will.......OMG the list goes on. 

The properties we toured were very old and in different stages of rehab, but I wasn’t particularly impressed by the rehab work, the contractors smoking indoors, or some of the uneven floors that they just decided to throw carpet over, hoping no one would notice.  

So my next option is to find some specialty markers and write in the address.Are these any thick, white or silver, truly all weather markers I can use for this purpose?

And I definitely agree with prior commenters who counted food stamps toward income - it bolsters against food costs either way.While I'm not currently managing any properties, an old friend from my college years rents out smaller units in and around Silver Spring, MD.

Not to mention the health risks involved with second hand smoke.

You could use the "silver tsunami" mantra that has been said, or you could look at the demographics for the area you plan to invest/open a facility in. 

OP is looking to handle the bookings themselves and have someone take care of all the issues after the guests check in (beeping smoke detector, toilet won't stop running, etc).