what does this mark mean on reed switch?
They don't.  Have  a broader look at reeds from other sources.  I have  a bunch of them here, and install them professionally for burglar alarms.  They either have no markings, or sometimes the manufacturer's details.  They don't have little black dots.  Can I suggest Google Images "reed switch"?  You'll see loads of examples, all without black dots. A reed switch is symmetric, non directional or un polarised.  They work either way round so don't require one end to be marked.

As to a getter.  No.  Getters are only for maintaining vacuum.  A reed switch contains an inert gas (typically nitrogen). The wiki entry mentions high voltage reed switches that operate in a vacuum, but I don't think that this is one of those.

It could be a testing mark, perhaps maybe. Could also be a spider.