Watermark placement? Were should I put my watermark?

Hello I am going to start making art commissions of cute fantasy type creatures.

My plan is to get at least 5 creatures made before I start and get them a few different looks to start with like different facial expressions and more.

I was wondering where should I put my watermark on the creatures when I advertise them without people being able to take them and remove my watermark?

Should I put it over the creatures or the main part of the area and make it fade a bit so people can still see the creature and what all there is?

Or should I make my watermark completely transparent?

Also I'll be making creatures ready to "Adopt" and want to put my watermark over them to keep people from taking them until they are paid for, so should I have my watermark faded a little so they can still see the adoptable creatures but still see the watermark? I know once someone gets one I'll move the watermark off the creature itself but still will have it where it can be seen.

Any advice and suggestions are much appreciated! Thanks in advance.