Is there any rule for writing transaction ID in the Deposit or Withdrawal Form?

Yes.

Please read the article completely for better understanding.

As per POSB CBS Manual Volume, writing of trans ID should be Red Ink on the upper right hand side corner of the Pay in Slip or withdrawal slip with Scheme Code.

POSB (CBS) Manual Rule No.9 : Pay in Slip - Deposit Form

SB7 Withdrawal Form - Using of Red ink on upper right hand side with Scheme Code

Hence, the transaction ID should be written on SB7 form like shown below

Counter PA should write Transaction ID on the upper right-hand corner of SB-7 in red ink prefixed  scheme name e.g. SB, RD, TD, MIS etc. 

All deposits presented at the counter of Post Office will be accompanied by pay-in-slips with counterfoil (SB-103) duly filled in by or on behalf of the depositor. The Counter Assistant accepting the deposit should check the entries in both parts to see that they agree in all respects and after transaction is done in Finacle CBS Application, note Name of Scheme and Transaction ID in red ink on the upper right hand corner of the Pay-In-Slip.. The date-stamp should be impressed at the marked place on both parts. The counterfoil will be signed, detached and handed over to the depositor or his messenger. The pay-in-slip will serve as a voucher for deposit. This voucher will be included in the Voucher Bundle along with other vouchers.