Most humbuckers are symmetrical and their sound does not change at all when installed backwards, but some have a slightly different sound if you install them in the opposite direction from normal. It’s not a matter of right or wrong, but a matter of taste for such a subtle difference, if you can hear the difference at all. Those models include the Air Norton™, Air Zone™, Evolution® neck, bridge and 7-string, FRED®, Humbucker from Hell™, DLX Plus™ neck and bridge models, Virtual P-90™, Blaze™ neck and bridge models and Tone Zone 7™.
The Steve’s Special™, the Bluesbucker® and the MegaDrive™ have distinctly different sounds if you turn them around, and there is no right’ installation direction. The Bluesbucker® is brighter-sounding with the adjustable screw coil towards the bridge, while the MegaDrive™ is brighter-sounding with the adjustable screw coil towards the neck. The Steve’s Special™ is brighter-sounding if the coil on the pickup’s cable exit side is toward the bridge.