As per the documents checklist, specifically
4. Documents referring to you and your spouse: a. Tax returns, bank accounts, leases, mortgages, or birth certificates of children; or b. Internal Revenue Service (IRS)-certified copies of the income tax forms that you both filed for the past 3 years; or c. An IRS tax return transcript for the last 3 years.
If your tax transcripts lists both you and your spouse over these 3 years then there is no need to supply anything else. If you filed separately such that neither of you are on a tax return together, then I would supply a bank statement from the beginning of year 1, then another for the beginning of year 2 then another for beginning of year 3 and the very latest statement. Sign them if you like but if the documents checklist / application doesn't say to do then why bother?