Welcome to AF! I'll move this to the X section for you so that the users there can assist with where to check for the watermark damage strips.
Under the battery door there's 2 white stickers with red x's on them. One is on the battery and the other is under the backing plate of the phone, there's a round view hole to the left when you are looking at the back. If those red x's are "bleeding" they've been wet.
