I would definitely report it. It is, plainly and simply, theft. It only happened to me once, and that was when I was staying at a very nice hotel in Banff. A breakfast credit was included in the price of the room, and every morning after dining we were presented with a zeroed out bill for our signature and room number. However, there was a spot for tipping, and so I always tipped on the pre-credit price as a room charge. When we checked out, our bill actually included copies of these signed receipts. I noticed for some reason my initials were written next to the tip line on each receipt. Curious, I asked the front desk what that meant. Surprise! Turns out that (unknown to me) the breakfast credit also paid for an 18% tip to the server. Servers were required to have guests initial any amount they put into the tip line to show that the guests understood that they were tipping over the 18% already allocated to the server.
So not only did our server conveniently not explain that to us (which I might have forgiven or passed off as absentmindedness), but his deliberate choice every day for 5 days to forge my initials showed it was premeditated. When I told the front desk what he'd done, I thought the hotel manager was going to blow a gasket. I was pretty irritated at the time, but it is still weird to think that it's very likely I got this guy fired. Correction: he got himself fired, but it's still strange. Despite that, I would still rat him and anyone else out who tried to steal money from me through the tip line. I also wouldn't just stop at disputing it to the credit card, I'd contact the business owner directly. Anyone who does this is likely stealing from the business as well.