You know your house is old if...

...knob and tube wiring can be found running throughout your house. Thankfully, it has been replaced with more modern wiring. But no one ever removed the old wiring.
Especially up in the bat infested attic.

So just what is knob and tube wiring, anyways?

Abbreviated K&T.

K&T was commonly used in North America from about 1880 to the 1930s. So it could have been installed in our house anytime during that time span.

It involves a single insulated copper wire that runs through the joists and studs insulated by porcelain tubes and knobs:
I found this tag up in the attic (where I find everything else, or so it seems).
It lists the name of the company that installed our knob and tube wiring. I just can't make it out. I'll try cleaning it up and get back to you all on that.