How to scratch out envelope 'Facing Identification Mark' (FIM) ?

I have been saving all the envelopes that I get within mail such as cell phone bills, credit card bills and any spam mail with return-envelopes. Consequently I now have a huge pile of clear window envelopes. I have been trying to reuse these envelopes and in that process discovered the significance of the pre-printed bar codes on such envelopes.

The most common lines are the bars on the envelope near the right upper edge and to the left of the postage stamp area. These bars are called 'Facing Identification Marks'. All the envelopes that I have saved have the FIN A bar code on them.

The following image shows the FIN bar code on a postcard.


So now when I reuse these envelopes, do I need to scratch the FIN bar code or should I leave it?

The USPS web site says:

A FIM must be printed on all letter-size BRM and on business reply labels affixed to letter-size mail. One purpose for FIMs is to face the mail as it is processed through the advanced facer canceller machine. The other purpose is to direct the mailpiece to either the optical character reader or the barcode sorter, depending on whether it has a barcode applied.

So, leaving it in will at the very least allow the sorting machine to now which way is face up. Wikipedia states:

FIM A is used for courtesy reply mail metered reply mail with a preprinted POSTNET bar code. In both of these types of mail, the postage is prepaid, either by a postage stamp in the case of courtesy reply mail or by a postage meter in the case of metered reply mail.

Since, my envelopes do not have a postnet bar code on them, I guess eventually the system will get confused and this may delay the sorting of my mail or worse, increase the chances of it getting lost.

I am still not sure as to what is the best way to strike out these bar codes and on the lookout for the information.

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