Even if I met all those standards, I will be discouraged to rent it because I may think somewhere between the lines, I don't qualify.

I have met all the tenants in the house except for one lady because she just moved in last month.

Reflective metal type labels are also available.

About an inch of concrete behind the tile walls with metal lathe embedded into the concrete.

Washer knob is already broken and it sounds like metal on metal grinding during the agitation cycle. 

These are mechanical systems that use a master key (a real, physical key) and a tool (a pointy metal toothpick thing).

I purchased a 3family home in Philly (it already had a system I think) big red metal circle and fire alarms on all hallway floors. 

However, they left some rust stains in the corner of the bathtub (what looks like from a metal can they had there), I've tried CLR, Lime away, bleach, etc. and I cannot get this to come out. 

While a metallic footprint consistent with a large metallic object present, the absence of a fill pipe or vent pipe necessitates the need to excavate the area with shovels.

@Joseph Caracappa  he started with a little Gestentner printing press were you had to put metal dies that wrapped around the drum then.. feed it paper and ink..