Shows a glowing icon and the name of any magic or enrage buffs on your target that can be removed with your Tranquilizing Shot. By default it uses the "dispel" sound effect from the SharedMedia_Causese sound pack addon. You can change it (or remove it) to another sound effect in the Actions tab of the weakaura.
Got original idea from Aywa's Purge WA ( https://wago.io/41Lx_qsWX ), but wanted something that also worked for enrage buffs. If you are playing a class with only magic purges, you should check out that one.
Note: Updated for Shadowlands, it used to be based on the pet's ability to purge in BFA