I'll speak up for my local here.
If a pledge was seen wearing letters of any sort..well..they'd have the letters ripped off of them so quick it'd make their head spin
The only time they are allowed to wear letters is during "hell week" in which the shirt says:
(front)
LOY
Pledge
Fall 2003
(back)Lambda Omicron Psi
(sleeves) Big & Little sis