Even in this day and age of email, social media, and electronic documents, the signature is powerful. If at all possible, the customer representative, project sponsor, and project manager should sign the SOW. This signature page should be dated and versioned identically with the SOW body. If an actual signature offends sensibilities, the PM should try to get an email approval. Worst case, get a verbal approval and send out a public email saying the appropriate parties have approved the SOW. The signature page must include some verbiage relating to approval of the items listed in the SOW, including financial responsibility.