the I-134 intructions state for proof of income, a letter on company letterhead showing present salary and date of empoyment. It only ask for the latest year of taxes(IRS 1040) but I have heard the last three years is a safe way to go. The w-2's would also serve as additional proof of income. The instructions say nothing about notarizing any evidence but it wouldn't hurt to take that extra step. Also, according to the instructions, this evidence needs to be submitted in duplicate and, of course, the I-134 must be signed and sealed under oath, (Notary Public). This is how I am handling mine.