To Watermark Or Not?

Ok, I decided yes.  I read a tutorial on Fox Hollow Cottage blog and it didn't seem very difficult.  I decided not to go back and put watermarks on all of my colored pencil paintings.  So, I'm starting with this one:

                                                        Old Courthouse, Old Glory 8 x 10 nfs

Not for sale, yet.  I'm entering it into the Midwest Color 2012 exhibition sponsored by the CPSA Chicago district Chapter.  This painting of the old courthouse in downtown St. Louis, MO. is a reflection in a nearby window. .

I've been taking photos all around the St. Louis area, for a series on local landmarks.  Here's my current work-in-progress:

I'm saving working on the Gateway Arch last - I want to make it stand out.  I fiddled with the watermark on this image, making it larger.  Do you use watermarks?