When you have 4/4 Pieces of a set, such as the Dragon Armor Set (2x Mob Heads & Perm Speed 2), it should say in chat that the buffs have been activated, because you don't know if they are actually working.
Example Messages:
&a(armor) buffs have been activated/applied
&c(armor) buffs from (armor set) have been deactivated/unapplied
Example Messages:
&a(armor) buffs have been activated/applied
&c(armor) buffs from (armor set) have been deactivated/unapplied
&aMagic Armor Set buffs have been applied
&cMagic Armor Set buffs have been unapplied
The messages could be changed, this is just an example. The messages could also list what buffs you have gotten from your armor.