The # or Hash Tag is for steering your page and Tweets in the direction of like minded people with the same interest as well as seeking them out. You must attach it directly to a word and that word can have no breaks such as #internalmedicine. If someone does a search for internal medicine your post will be at the top of the search for a time and will eventually drop down like threads on a forum. You can also use this in your bio to lead similar people to follow you such as an Alabama Football fan putting #AlabamaFootball and #Rolltide in his bio. Beware though, you will get lots of spam if you put Doctor or Internal Medicine.
