There are a few hashtags used by the MLP: FiM Twitter Fan Club. If you're going to take part in the RP, it's a good idea to keep an eye out for them, and to set your twitter client to pick them up when they're used. There aren't many, but these are a couple of the most used:

  1. MLT: Used by fans and the roleplay group alike. When used by one of the main six or Mod, it's usually to get the attention of the group. Don't over-use it in RP.
  2. PVweather: Used to signify what the weather in Ponyville will be like. Sent twice daily at approximately 9-10am and 7-8pm Eastern Time by Twitter-profile adp_pvweather, typically managed by Twitter-profile adp_Dashie (It's a scheduled message that will appear anywhere between 9 and 9:30. You think Rainbow wakes up on time?). Also used for weather abnormalities and storm notifications.
  3. PVnews: Used by Twitter-profile adp_pvnews to occassionally announce news events happening around Ponyville. Usually painfully punny and absolitely alliterating.
  4. MLPflag: Used to flag a tweet that violates ou terms. Report it to Twitter-profile the mod if it happens.
  5. foalswag: A silly hashtag used by foal characters for laughs.
  6. Dream: Used to let people know that what is happening to you is really what's hapeening in your dream while your character is sleeping.