So for me, there are a few different types of notifications (assuming that's what we're talking about, not vibrations for phone calls or alarms)
- Important/Non-recurring Reminder (Text message, reminder to take cookies out of oven)
- Not important/Recurring Reminder (E-mail [because we get so many of them], reminder to walk the dog)
- Not even close to important (daily weather alert?)
And basically I think that the length of the vibration pattern should reflect that.
So maybe a 1 second pattern for important, 0.5 second pattern for non-important, and just no vibration at all for anything that isn't even close to important
As to what the exact pattern should be-- as others have mentioned, that doesn't really have a standard AFAIK. But I only have the apple watch, so I couldn't speak to if there is a standard or not.
One thing to note is that you can add some feeling into the vibration pattern. Quick staccato beats give a happier mood, while a longer legato pattern gives more of a sad mood