Given a speaker driver with no obvious markings, how should one determine the connection polarity?
I'm aware of the method of using a DC voltage to see which way the cone moves, (noise - Does DC translate to sound? - Sound Design Stack Exchange), but that method could potentially damage low power speakers.
With a single speaker configuration, in my own opinion it doesn't really matter, however this is not the case in a multi-speaker configuration where relative signal phase between channels matters a great deal.
However, it is the relative signal phase that matters, not absolute signal phase. As long as (in, say a stereo configuration) both speakers are wired identically (same phase) you will have a working system that is 'in-phase'.
It is fairly simple to aurally detect speaker configurations that are in- or out- of phase. This should be done by sending a mono signal to both speakers in the configuration and listening for whether the stereo image is centered or not. Alternating the phase of one of the speakers periodically can also assist in identifying the correct configuration.
Checking a speaker system for phase has to be done through an amplifier as well as via the speaker. It is likely a rare occurrence that an amplification powering a stereo speaker system will be internally mis-phased, so it's a safe assumption that you can wire in and out of an amplifier identically and have proper phase characteristics.
Any thoughts of laying DC through a speaker should be strongly discouraged due to the danger of damaging the speaker coil through excessive heating.
