I just did scraping of my bike 2 months back.
The procedure is this:
1) Go down to LTA @ Sin Ming bringing along your vehicle's
documents - LOG CARD (impt) and your IC. You can
authorize someone else to act on your behalf by passing all
documents to him/her together with your letter of consent. That
person must bring along his/her IC too.
2) Approach the Service Counter which you can see immediately when
you enter LTA, ask for a Quene Number for Counter 13 or
14.
3) When your number is called, tell the LTA staff that you want to
scrape your vehicle.
From that onwards, the staff will guide you. Remember to obtain
from him/her a Derage Form aka Deregistration
Form.
You can either bring your bike to authorized scrapeyards (locations
ask LTA - 1800 - 225 5582) or engage a towing service which they
will charge you for doing it for you.
By scraping bike, you won't be able to get back any liquid sum of
your bike. You are only entitled to the remaining rebate of your
COE which you can use it for your next purchase of a vehicle or you
can transfer it to anyone else for a $10 transferring fee; alas,
selling it to others.
Hope my infos help.