RE: Can anyone tell me if there is IRS rule requiring Officer's SSN on 990 (Part IV - Taxpayer Signature).

Wait a minute.  Form 990 Part IV is Checklist of Required Schedules.   Is the question about one of the thirty-something questions has to do with SSN?

The Signature block is Part II.  Part of the earlier discussion mentioned PTIN.  Is the question about PTIN in Part II?

Or is it about the entries for Officers (in Lacerte - Screen 2), where the bottom field is SSN.  In Lacerte, the instructions specify: SSN (Used for California reporting, others options.)

On a separate note, be aware that Form 990's are available on the CA Attorney General's Charitable Trust website.  Even if the IRS blocks certain info, you may want to check if AG website does the same.   Schedule B is NOT supposed to be open for public inspection.  In the past, I have seen Sch B on certain websites.

I'm confused.