Well I think making necklaces little 'achievement' decorations works to a point.
Right now we have
Gold Chain -> "I am Rich"
Hunting Necklace -> "I use the store"
I'm sure we can come up with a dozen or so others that can only be obtains if the player does do 'certain' achievement-like things. The problem and beauty is that they will always find their way into circulation from those who raid or kill the achievers.