*UPDATED AUG 2018*
None, but you will need a Twitter handle; <—Click here to read why Twitter is useful!
What to do:
If you are searching for a resource, or like minded colleagues, or advice or just some interesting things to read, you may want to search using a #:
“A #hashtag is a way to aggregate tweets that are appended with a hashtag. Picture it like a magnet that attracts all messages categorized by that topical word or phrase.” (Ref.)
Here are a list of hashtags that are subject/phase specific! Check them out…
Add some that you know about/use?