Hi girls. Sorry to crash your board.
We had the same problem the semester after I was initiated. When we were discussing it, I mentioned that the *biggest factor* in my remembering to wear MY pin was knowing I'd see older sisters on campus.
Hearing the girls say, gently but seriously, "Why aren't you wearing your pin?" made me realize how important this was to THEM. Pledging the sorority was important to me -- I wanted to earn the respect of the older sisters. We weren't REQUIRED to wear the pin, either, and we had no hazing -- I just felt like I'd been allowed into something really special, and wanted to feel like I deserved it.
If that makes any sense?
At any rate -- you might consider mentioning it to the other sisters and have them remind your new members. The trick is to do it kindly without being like "HEY PLEDGE! WHERE'S YOUR PIN?! FRY LIKE BACON!" etc. *ahem* Anyway.

Betcha it works perfectly.
good luck!
Greek love,
Jacquelyn.