Validation should check the signature, too

Based on that question, I would suggest that the validation of a database should check the signature string, too.

As John and Mark have explained in comments on this answer, some bytes in the first database page (the "signature") state whether the database file is valid or not.

Well, if the signature is invalid, validation of the database should give an error, too.

Nevertheless, the following statement running on my (not successfully upgraded) database (under 12.0.1.3356) returned no errors at all:

calldbo.sa_validate()

That just seems wrong.

Side effect: If it had given an error, the maintenance plan would not have overwritten a valid database backup.