Phi Beta's pledge pin is a small gold Phi. Nothing too exciting, but meaningful to those wearing it.
And since our badge is a stacked Phi & Beta, I suppose it suggests the official badge, also.
http://www.phibeta.com/graphics/jewelry/pledge.jpg
Although, when I pledged, there weren't enough for everyone (they take forever to come in & arrived about 2 weeks after our pledging ended) so we had a gold & violet ribbon tied together so everyone had the same thing. The cool thing about that was that we got to keep them. The real pledge pins are returned upon initiation.