In my experience, buyers never initialled OR signed the original Warranty Deed -
Title, at times, will make a copy of the original for the buyer's review and have them initial that they accepted and approved the deed - but it's on the copy for title's file only - heading off any future problems where owners say "that's not how I took title", blah blah. However, the original, signed by the Sellers and recorded in the property records (county, city/town, district, wherever it's recorded in the pertinent state) IN MY EXPERIENCE has never been signed or initialled by the buyers.
P.S. I should add my experience is 10 years here in FL as a signing agent and 25 years in CT as a closing paralegal. All that said, just follow instructions of hiring party Me, personally, if I'm not told to have them initial, or there is no small line on the deed for their initials, I would not take it upon myself to have them initial. JMO.