How one would determine polarity of Altec 808-8G ?

"I also noted that the metal nut/cap that clamping the speaker cable onto the speaker had an dash stamped on top."
After looking at different Altec HF drivers. I found that the dash was actually a number 1 and the other cap had a number 2 stamped on it. I gathered that number 1 is positive and number 2 is negative.

Thanks for your inputs. I used 3 volts and observed the diaphragm moved forward. It easier to see diaphragm movements if you let the light shinning on the diaphragm at certain angle. I also noted that the metal nut/cap that clamping the speaker cable onto the speaker had an dash stamped on top. It looked like a negative polarity sign but it was on the positive speaker tap.

Apparently this Altec speaker (I am not familiar with) is very sensitive to applied DC voltage so proceed cautionsly.

A safe approach involves use an ohmmeter set on the low [R X 1] scale, which was a nominal 1.5 vdc output. The output impedance of the meter helps reduce the applied voltage/current surge to the voicecoil. A 1.5V battery with a flashlight bulb connected in series should also be a safe current limiter if you have no meter, but do buy a at least an inexpensive DVM which is pretty much mandatory for speaker work anyway. Limit the time duration of the applied dc source voltage to only as short a time as necessary.
The aforementioned regarding polarity behavior is accurate.

I was told to use a 1.5V battery, NOT a 9V battery for testing a speaker's "polarity" (phase).

WARNING!!!DON'T DO THIS!!!!!(What was recommended by Joe A.) I'm sure he meant well, but isn't familiar with the Altecs. I have put low voltages through an Altec 802-8g, on the order of .5 volt and used a magnifier to observe displacement, and the terminal markings are correct - the red is indeed positive. Looking from the back of the driver this would be the left bottom push terminal. Hooked up accordingly, this would give the dome a positive displacement down the throat of the driver, out into the horn.

Use a 9 volt battery -- the kind you'd find in a garage-door opener. Touch the battery terminals (or use short lead wires, if necessary) to the spkr terminals. When the Plus battery terminal meets the Plus spkr terminal, the speaker cone will move FORWARD. In reverse polarity, it will move backward.