Identifying the pins of an AC lamp
The data sheet shows the leads for each termination configuration, and for all the other terminations the anode/positive is the top lead (red or longer) so I would be surprised if the brass lugs are not the anode and the tinned lugs the cathode in the DC variants.

As yours is the AC variant, and assuming it's got two LEDS in different directions, diodes to prevent backward voltage getting too high and resistors for current limiting, it should start glowing with a few volts DC across it. The forward voltage of the diodes could mess up multimeter resistance readings. I'd guess that each of the tinned pins corresponds to one LED and you can either connect it for either full wave or half wave.