Silly question about Baluns....
 

Do they have polarity? Would signal be affected if you hooked them up backwards? I don't really see anything on them that looks like a polarity key but then again I haven't really looked at one close, I just hook them up and forget about them.

Not silly IMO...
 

Yes, baluns have polarity. But when used in a typical installation, the polarity is irrelevant. When used to connect an antenna to coax or coax to tuner, you are correct to An uncommon application where polarity would matter is joining or stacking identical antennas. This is so uncommon that you will probably not ever find a balun with polarity marked or labeled. If you are interested, Antenna Stacking & Transformer Phasing Tutorial

Balun / Matching transformer /
 

Have no polarity when used to match 300 to 75 and 75 to 300 in a typical tv antenna installation. The balun can be turned around and used in the other direction. An example is , a Winegard HD7082P antenna has 75 impedance connection and a preamp has a 300 impedance input , the coax from the antenna is connected to the 75 impedance end of the balun and the 300 impedance end of the balun is connected to the input of a preamp that has a 300 impedance input. Or it could be the other way around , the antenna has 300 impedance connection and the preamp has the 75 impedance input. A typical balun is a few turns of wire on a ferrite core. The inexpensive ones are a metal tube and the inside is easy to slide out of the tube , take it apart and have a look.