In April 2004, the ABA wrote a letter that indicated that they had spoke with each of the regulatory agencies concerning confusion surronding the Evidence of Intent to Apply issue. One of the ABA's statements was that a signed Fannie Mae 1003 application is sufficient evidence of intent. The idea is that if the borrower and co-borrower sign the application (and this would be true for any and all applications) you have all of the evidence you need. Think about it: Why else would someone sign an application?
I know that the signature represents an attestation to the accuracy of the info. provided, but the applicant's name is under the heading "Borrower" or "Applicant" and the co-applicants is the same.
Reg B does not require signed applications, let alone any special type of application - even on home loans [see the Commentary to ยง202.4(c)#1]. Loan officers are required to document information provided, including who the applicants are (there's your evidence of intent to apply).
This is the type of issue that we will be discussing during the webinar on Wednesday. You can sign up for it
here